1. The activity of N-sulphotransferase (N-ST) with desipramine (DMI) as substrate was measured in 118 human liver specimens, in platelets obtained from 105 subjects, in 12 specimens of human ileum and colon mucosa and in five specimens of human kidney and lung. 2. N-ST activity ranged between 5.71 and 157 pmol min-1 mg-1 protein in human liver and between 0.27 and 17.3 pmol min-1 mg-1 protein in human platelets. 3. Probit analysis was compatible with a unimodal distribution of the data from both liver and platelets. 4. The frequency distribution histograms of N-ST were asymmetric, with a positive skew in data from both liver and platelets. The mode, median and mean of N-ST were 16.4, 30.2 and 40.4 pmol min-1 mg-1 protein in liver, and 2.12, 3.61 and 3.82 pmol min-1 mg-1 protein in platelets, respectively. After logarithmic transformation of N-ST activity, the frequency distribution histogram was symmetric for data from both liver and platelets. 5. In extrahepatic tissues, the average (+/- s.d.) N-ST activity (pmol min-1 mg-1 protein) was 22.2 +/- 22.8 (ileum), 20.9 +/- 26.9 (colon), 12.4 +/- 5.5 (renal cortex), 9.3 +/- 2.8 (renal medulla) and 4.2 +/- 1.1 (lung). N-ST is widely distributed in the body and the intestine is the extrahepatic tissue with the highest N-ST activity.