As the name implies, a phase 0 trial precedes "phase I" testing, traditionally the first step in the process of human drug testing.

'Phase 0' Trials Aim to Speed Cancer Drug Development -- Even after years of painstaking research and testing, only a small percentage of cancer agents make it from the laboratory to the patient. "We want to find out if they're ineffective in the smallest number of patients and get definitive information as benedetto in the development process as possible," said Dr. Doroshow, director of the division of cancer treatment and diagnosis at the National Cancer Institute in Bethesda, Md. So scientists have come up with a way to weed out the duds earlier in the process and speed good medications to the marketplace. The new model, a so-called "phase 0" clinical trial, promises to streamline the costly and time-consuming drug development process, helping to deliver good drugs to people who need them more quickly.

In a phase I study, the goal is to determine the best way to administer a drug and the maximum dose tolerated with the fewest.