Antineoplaston AS2-1 and Antineoplaston AS2-5 are degradation products of Antineoplaston A10. The initial hydrolysis of Antineoplaston A10 (3-phenylacetylamine-2, 6-piperidinedione) yields phenylacetylglutamine and phenylacetylisoglutamine. When hydrolysis is carried further the products of the reaction include phenylacetic acid, glutamic acid and ammonia. Sodium salts of phenylacetylglutamine, named Antineoplaston AS2-5, phenylacetic acid and a mixture of phenylacetylglutamine and phenylacetic acid in the ratio of 1:4, named Antineoplaston AS2-1, were submitted for tissue culture and animal toxicity studies. Tissue culture tests were carried out on breast carcinoma cell lines HBL-100 and Ki No. 1 and the results were expressed as the percentage of colony reduction based on control. Acute toxicity studies were done on a group of 88 HA/ICR Swiss mice with each of these formulations. An additional group of 160 mice was used for chronic toxicity studies of Antineoplaston AS2-1. In chronic toxicity studies the mice were injected with 92.3 mg/kg, 553.8 mg/kg and 1107.6 mg/kg of Antineoplaston AS2-1 intraperitoneally for 365 days and subjected to complete physical, gross pathology and microscopic examination. LD50 for tested formulations were as follows: Antineoplaston AS2-1: 2.83 g/kg, Antineoplaston AS2-5: 2.90 g/kg and phenylacetic acid: 2.71 g/kg. The results clearly demonstrated that Antineoplaston AS2-1 has interesting antineoplastic activity in tissue culture of breast carcinoma, and low acute and chronic toxicity in mice. Antineoplaston AS2-5 does not show significant activity in tissue culture of breast carcinoma HBL-100 and only slight antineoplastic activity in Ki No. 1. Both formulations were submitted for phase I clinical testing in cancer patients.