OUTLINE: This is a multicenter study. Patients receive PSA-3 peptide vaccine emulsified in Montanide ISA-51 subcutaneously in 2 sites on days 1, 8, 15, and 22 in the absence of unacceptable toxicity. Patients who show an immune or prostate specific antigen (PSA) response are followed until disease progression, defined as a diminution or disappearance of an immune response or 2 consecutive increases in PSA over the nadir. Patients are eligible for a second series of injections at the time of progression.