Antineoplastons, which were firstly described by Burzynski, are naturally occurring peptides and amino acid derivatives which control neoplastic growth. We conducted a toxicological study of the Antineoplastons A-10 and AS2-1 in combination with other anticancer agents or radiation in 42 patients, 46 tumors with terminal stage cancer. Antineoplaston A-10 oral formulation and A-10 injectable formulation was administered in 14 and 25 patients respectively. The maximum daily dose was 10 g and 40 g, respectively and the longest term of administration was 610 days and 67 days, respectively. Antineoplaston AS2-1 oral formulation and AS2-1 injectable formulation was administered in 33 and 10 patients, respectively, the maximum daily dose was 12 g and 30 g, respectively, and the longest term was 1070 days and 25 days, respectively. The major adverse effects that may have been related to these agents as used in combination with other conventional chemotherapeutic agents or radiation were general weakness, myelosuppression, and liver dysfunction, but these effects were not seen when either Antineoplaston was administered alone. The minor adverse effects observed in single use of either Antineoplaston A-10 or AS2-1 were excess gas, maculopapullar rash, fingers rigidity, reduced cholesterol, reduced albumin, increased amylase, eosinophilia, increased alkaline phosphatase, headache, hypertension, palpitation, peripheral edema but these adverse effects did not limit to continuation of either agent. The evaluation of the usefulness of the Antineoplastons in combination therapy based on the imaging findings during the course of treatment revealed disappearance or measurable shrinkage of the tumor lasting more than one months as visualized by magnetic resonance imaging or computed tomography was seen in 15 tumors (32.6%). No increase in size of tumor for more than 3 months was observed in 8 (17.4%). The mean survival time of these patients was significantly longer than that in patients with tumors showing progressive increasing (17.52 + 3.31 months vs 4.80 + 0.65 months, p < 0.005). Antineoplaston A-10 and AS2-1 are less toxic than conventional chemotherapeutics and they were useful in maintenance therapy for cancer patients.