Antineoplastons, first described by Burzynski, are naturally occurring peptides and aminoacid derivatives which control neoplastic growth. Antineoplaston A10 (3-phenylacetylamino-2, 6-piperidinedione) is the first chemically identified antineoplaston and when it is administered orally it is hydrolysed in pancreatic juice to phenylacetylglutamine and phenylacetylisoglutamine in the ratio of 4 to 1. These metabolites are water soluble and have antitumor effect, they are further degraded to phenylacetic acid. The mixture of phenylacetylglutamine and phenylacetylisoglutamine in the ratio of 4 to 1 was formulated as Antineoplaston A10 injectable formulation. The mixture of phenylacetylglutamine and phenylacetic acid in the ratio of 1 to 4 was also shown to have antitumor effect in tissue culture study, then formulated as Antineoplaston AS2-1. The reported cytostatic inhibitory effect of A10 on human hepatocellular carcinoma cells and differentiation inducing effect of AS2-1 on various tumor cells suggest potential benefit for the treatment of human hepatocellular carcinoma since this tumor recurs frequently despite initial successful treatment. We report here the effects of Antineoplaston A10 and AS2-1 on cell proliferation, cell morphology, cell cycle, and DNA in human hepatocellular carcinoma cell lines. Both agents inhibited cell proliferation and increased the number of cells in G₀ and G₁ phases and Antineoplaston AS2-1 induced apoptosis, we also describe our clinical experience of a hepatocellular carcinoma (HCC) patient whose tumor, after incomplete transcatheter arterial embolization (TAE) for a 7 cm^*7 cm HCC, has been stable for more than 15 months during which time he has been taking Antineoplaston AS2-1 continuously without any serious adverse effects.