PRIOR CONCURRENT THERAPY: Biologic therapy: No prior biological response modifier therapy Chemotherapy: No prior chemotherapy (including suramin) Endocrine therapy: At least 1 year since any adjuvant or neoadjuvant hormone therapy No more than 4 months of therapy as part of initial prostate cancer therapy Prior finasteride for benign prostatic hypertrophy allowed No systemic steroids other than hydrocortisone (steroid inhalers allowed) Radiotherapy: At least 4 weeks since radiotherapy (90 days since strontium) Surgery: Recovered from prior surgery