Spontaneous motor activity was monitored in rats at various times, up to 14 weeks, after portacaval anastomosis (PCA) or sham operation. Total 24 hour activity scores rose significantly after PCA and remained significantly higher than those of sham operated rats for twelve weeks. After PCA, activity during the twelve hour lighted period was greatly increased, whereas dark period activity was unchanged. Increased activity in the light period was found to be well correlated with the degree of elevation in brain concentrations of tryptophan, tyrosine, phenylalanine and glutamine. These results are consistent with previously reported EEG studies and suggest that motor-activity measurement may facilitate the correlation of biochemical changes with behaviour in rats with portal systemic shunting.