Antineoplaston A3 is an oxidized mixture of small and medium size peptides and amino acid derivatives isolated from human urine. The purpose of this study was to evaluate the growth inhibitory effect of Antineoplaston A3 on cancer cells in vitro and its toxicity in mice. The growth inhibitory studies were carried out on breast carcinoma cells HBL-100. The cells were plated at 1000 cells per flask in L-15 medium and supplemented with 10% foetal bovine serum and antibiotics. Two different experiments were performed: to study dose response; and to investigate duration exposure. To establish dose response, Antineoplaston A3 was added to each flask to a final concentration of 0.05, 0.1, 0.2 and 0.4 mg/ml. Two flasks in each test were added with the same amount of medium to serve as control. The flasks were incubated at 37 degrees C for 6 days, then fixed and stained, after which colonies were counted. Results were expressed as percentage of control. In duration exposure experiments Antineoplaston A3 was added to the final concentration of 0.4 mg/ml. After 24, 48 and 72 h of exposure to Antineoplaston A3, the flasks were returned to normal growth medium and colonies were again counted. Dose response to Antineoplaston A3 was as follows (average of 3 replications +/- standard error): 0.05 mg/ml, 100% +/- 0; 0.1 mg/ml, 79.0% +/- 14.4; 0.2 mg/ml, 4.3% +/- 6.6; 0.4 mg/ml, 0% +/- 0.(ABSTRACT TRUNCATED AT 250 WORDS)