Antineoplaston AS2-1 is a mixture of two products of hydrolysis of Antineoplaston A10 and consists of sodium salts of phenylacetylglutamine and phenylacetic acid in the ratio of 1:4. Antineoplaston AS2-1 injections were administered to 20 patients diagnosed with 21 types of neoplastic diseases. The patients' diagnoses included: lung cancer, stage III, 4 cases; colorectal, stage IV, 3; breast, stage IV, 2; breast in remission, 1; glioblastoma, 3; head and neck, stage IV, 3; uterine cervix, stage IA, 1; chronic myelocytic leukaemia, 2; lymphocytic lymphoma, stage IV, 1; and leiomyosarcoma of the uterus, stage IVB, 1. Antineoplaston AS2-1 was administered every 6 h i.v. through subclavian vein catheter. The treatment was administered from 38 to 872 days. The highest dosage taken was 160 mg/kg/24 h. The treatment was associated with minimal side-effects, including slight nausea and vomiting in one patient, mild allergic reaction in the form of maculopapular rash in another patient and moderate elevation of blood pressure in an additional patient. One patient developed febrile reaction and three patients had mild electrolyte imbalance. Only one patient showed slight decrease of WBC. Desirable side-effects included improved healing of chronic atrophic ulceration. The response to the treatment included 6 complete remissions, 2 partial remissions, 7 cases of stabilization and 6 cases of increasing disease. Three patients are alive, well and free from cancer 5 years after the beginning of the study. The hypothetical mechanism of action of Antineoplaston AS2-1 as an anticancer agent is described.