As part of an evaluation of the Spanish brush goat (Capra hiricus) as an anephric animal model, free amino acids were determined in plasma before and after 4-hour hemodialysis periods for 30–90 days following nephrectomy. The 72 liters of dialysate used in 4 h contained 15–17 mmol free amino acids in about the same proportions as in pre-dialysis plasma. Acid hydrolysis of deproteinized dialysate fluid released an additional 20 mmol amino acids, with much of the increase due to bound glycine. Despite the loss of some 5 mmol into dialysate, essential amino acids in plasma were unchanged during dialysis, indicating rapid replacement from some intracellular source (probably via breakdown of tissue protein). Some nonessential amino acids, particularly glycine and alanine, were considerably lowered by dialysis, suggesting that synthesis is required for maintenance of normal concentrations. Essential amino acids in predialysis plasma declined soon after nephrectomy and continued to fall during the ensuing 2–3 months, but most nonessential amino acids remained at about control levels. Both valine and tyrosine were decreased in the anephric animal, so the valine: glycine and tyrosine: phenylalanine ratios were lower than in controls. The general similarity between these data and those found for many uremic patients suggests that the anephric goat may provide a convenient model for study of negative nitrogen balance and other processes known to occur in u