The regulation of 1-cell mouse embryo development in culture by amino acids was investigated. When the 20 amino acids in Eagle's medium were present, blastocyst formation at 72 h (9%; p < 0.01), and blastocyst cell number (66; p < 0.05) and hatching (45%; p < 0.05) after 96 h of culture were significantly increased, compared to control embryos grown in the absence of amino acids (0%, 60, and 23%, respectively). The beneficial effect of Eagle's amino acids was attributed primarily to the non-essential group. In the presence of non-essential amino acids, blastocyst formation (54%; p < 0.001) and cell number after 72 h of culture (33; p < 0.05), and blastocyst cell number (69; p < 0.01) and hatching (68%; p < 0.01) after 96 h of culture were all significantly greater than for embryos cultured with all amino acids (9%, 26, 66, and 45%, respectively). In the absence of glutamine, essential amino acids significantly reduced blastocyst cell number after 96 h (53; p < 0.05). Continual culture in the presence of amino acids reduced the cleavage rate after around 72 h of in vitro culture; this decrease was not observed in the absence of amino acids. Transfer of embryos to fresh medium after 48-72 h of culture resulted in increases in the percentage of blastocysts formed and in blastocyst cell numbers. These data are consistent with the build-up of an inhibitory compound in the medium, possibly ammonium, an end-product of amino acid metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)