The pattern of depletion and appearance of a mixture of amino acids by single porcine blastocysts incubated in two different media has been determined non-invasively using high performance liquid chromatography. Zygotes were produced by the in vitro fertilisation of in vitro-matured, abattoir-derived immature oocytes and cultured in medium NCSU 23 with or without amino acids. Embryos grown in the absence of amino acids up to the blastocyst stage were transferred to amino acid-containing culture medium for measurement of turnover (Experiment 1). Blastocysts grown in NCSU 23+amino acids were transferred into fresh droplets of the same medium (Experiment 2). Although the specific pattern of amino acid production and depletion varied between experiments, a general pattern emerged, with arginine being significantly depleted (p<0.001) and alanine consistently appearing in the media, in quantities that varied depending with culture conditions. The data suggest that arginine is important during porcine blastocyst development, most likely contributing to the formation of nitric oxide and polyamines and that alanine is produced as a means of disposing of excess amino groups. A model for the interactions of amino acids during porcine early embryo development is proposed. The profile of amino acid metabolism by porcine blastocysts is qualitatively and quantitatively similar to that given by human embryos during the morula:blastocyst transition suggesting that the porcine blastocyst is a good model for the human.