This study assess the effects of oral BCG, as a single agent, on tumor progression and on cell-mediated immune function in patients with metastatic malignant melanoma. Thirty patients were studied including 22 with measurable metastatic lesions and 8 with no detectable disease, following treatment of metastases by surgery, radiotherapy, or 5-(3, 3-dimethyl-1 -triazeno)-imidazole-4-carboxamide (DTIC; DIC). Oral BCG was given in doses of 120--240 mg, 1--3 times per week for periods ranging from 9 to 80 weeks and to total doses of from 1.2 to 20.1 gm. Patients were assessed by direct measurements of tumor mass, PPD skin test and in vitro blastogenic responses to PPD PHA. Of the 22 patient with measureable disease, 19 showed tumor progression and none showed regression of any lesion. Of the 8 without apparent disease, 5 remained stable and 3 had tumor recurrence. Of the total group of 30 patients, 8 showed some increased sensitivity to skin testing with PPD. Of 19 tested, 3 showed an increased PPD response in vitro, while 3 showed a decreased response. Six of 20 tested showed an increased PHA response in vitro. Oral BCG alone was not effective as an antitumor agent in patients with metastatic malignant melanoma.