The relationships between the serum concentrations of amino acids, the volume of irrigating fluid absorbed and symptoms of glycine toxicity were analysed in 18 patients who had undergone transurethral resection of the prostate and in whom intravascular absorption of irrigating fluid containing 2.2% glycine had been recorded. A mean of 7% of the transferred glycine could be detected in the serum within 10 min of irrigant absorption. The half-life of glycine in serum was twice as long when the volume of irrigant absorbed exceeded 1500 ml (100 min; n = 6), and the serum levels of alanine, aminobutyrate, proline and serine were significantly more elevated, than when the volume of irrigant absorbed was between 900 and 1300 ml (n = 6). Where the amount of glycine transferred exceeded 0.5 g.kg-1, symptoms of glycine toxicity developed, their onset coinciding with a rapid increase in the serum levels of non-essential amino acids other than glycine.