As crime-solving wizards on TV’s top-rated drama, the stars of CSI steep themselves in blood, bullet holes and (very) gross anatomy.

This past summer the cast of CSI: Crime Scene Investigation did what you’d expect anyone from a major hit series to do. They kicked back and forgot about the inanimate parade of bruised, gouged, mutilated and (on one memorable occasion) liquefied corpses that form the dramatic center of the CBS show’s high-tech forensic sleuthing. Costars Jorja Fox, Eric Szmanda and Gary Dourdan all vacationed together in Paris. Evanston, Ill., native William Petersen took in a Chicago Cubs baseball game with six CSI grips from L.A.

Meanwhile Marg Helgenberger, 43, went on a busman’s holiday from hell: She’d been worried that the show’s phenomenal popularity - signaled by its own new spinoff, CSI: Miami, teaming NYPD Blue alumni David Caruso and Kim Delaney - might be taking the edge off her performance as intrepid detective (and ex-stripper) Catherine Willows. So she spent a night with Las Vegas’s own crime scene investigators, the inspiration for the series. The unit was called to a casino hotel to check out a corpse, male, in his 30s, dead of drugs and alcohol. “You get a sense of the fragility of life,” says Helgenberger, seated near a photo of her son Huey, 12, in her trailer on the set in Valencia, Calif. “But I also came away with a sense of what heroes these people are. They do a job most people couldn’t or wouldn’t do, and make a difference solving crimes.”

As of July, Helgenberger was back on the set for CSI’s third season, which kicked off Sept. 26 with its best ratings ever. An audience of 30 million tuned in for the adventures of this savvy, cast-iron-stomached Vegas forensics unit led by the obsessive Gil Grissom (Petersen, 49), with an assist from a team that also includes Warrick Brown (Dourdan, 35), Nick Stokes (George Eads, 35) and Sara Sidle (Fox, 34). Their cases are peppered with grisly details - an old lady devoured by her cats, a cheerleader disemboweled on a soccer field - and discussed with such intimidating jargon as “phenolphthalein” (a chemical that detects blood) and “epithelial” (skin cells). “Most of these terms are in Latin,” says Petersen. “But we learn as we go along.”

They learn fast. The show, which has supplanted ER as TV’s top-rated drama, is now famous enough that when Dourdan and Eads last year promoted CSI in Buenos Aires, where the show airs, local police decided to take the stars down a peg. “They showed us tapes of autopsies to see if we would crack,” Dourdan says. “We didn’t.”

Far from being queasy, the cast seems genuinely curious about the show’s morbid matters. Petersen - who is coexecutive producer and costar - unwinds by plowing through the dense prose of The Future of Life by forensic entomologist Edward O. Wilson. One shelf of Helgenberger’s colorfully decorated trailer includes Practical Homicide Investigation. The set’s atmosphere is hardly funereal, though. Some days Fox, Dourdan, Eads and Robert David Hall (who plays coroner Albert Robbins) bring out guitars for an off-camera sing-along of folk and blues, and Paul Guilfoyle, 53 (police captain Jim Brass), is considered a reliable cutup. Helgenberger arrives already chilled out. “I did yoga at 4:45 a.m.,” she says.

All around them, however, is the presence of death. There’s the lab (stocked, for verisimilitude’s sake, with several million dollars’ worth of equipment, including a $500,000 ballistics identifier) and Robbins’s morgue. “One of the treats for me,” says Hall, 55, “is what our special effects guy will do to the corpses.” The cadavers are actually actors, made up to look seriously dead and damaged. And all that blood? It’s Karo Syrup, “and it tastes like peppermint,” says Eads.

Even though the gore is fake, Jorja Fox and Eric Szmanda, who plays DNA tech Greg Sanders, could do with a little less of it. They will never again make the mistake of eating pizza before a forensics scene. “I started feeling nauseous,” says Fox. “I don’t think I could ever be a CSI.”