Sulfobromophthalein excretion and plasma ammonia and serum bile acid concentrations were measured in 11 dogs with portal vascular anomalies. The fasting serum bile acid concentration was increased in all 11 dogs (78.9 +/- 16.1 mumol/L; normal, 2.6 +/- 0.4 mumol/L). For values measured in 8 dogs, the 2-hour postprandial serum bile acid concentration was increased further (177.0 +/- 26.4 mumol/L; normal, 7.6 +/- 2.3 mumol/L). The fasting plasma ammonia concentration was markedly increased in all 11 dogs (246.9 +/- 40.3 micrograms/dl; normal, 27 to 15 micrograms/dl). Thirty minutes after the oral administration of ammonium chloride, the plasma ammonia concentration was increased further in the 7 dogs (510.7 +/- 45.5 micrograms/dl; normal, 57.5 to 20.5 micrograms/dl). Results of the sulfobromophthalein excretion test were abnormal in 10 of 11 dogs (12.3 +/- 1.4%; normal, less than 5% retention after 30 minutes).