1 Phenol- and catechol- sulphotransferase activities were measured with p-nitrophenol and dopamine as substrates in platelets obtained from 100 newborns and 100 healthy adults. 2 Mean +/- (s.d.) estimates of catechol sulphotransferase activity were 7.07 +/- 5.93 (adult) and 13.3 +/- 6.42 (newborn) pmol min(-1) mg(-1) protein, respectively (P < 0.001). The coefficients of variation were 84% (adult) and 48% (newborn). The frequency distribution of sulphotransferase activity was symmetric and did not deviate significantly from normality in newborn platelets, but was positively skewed in adult platelets. 3 Mean +/- (s.d.) estimates of phenol sulphotransferase activity were 3.01 +/- 3.21 (adult) and 4.80 +/- 4.34 (newborn) pmol min(-1) mg(-1), respectively (P < 0.001). The coefficients of variation were 107% (adult) and 90% (newborn). The frequency distribution of sulphotransferase activity was positively skewed in both newborn and adult platelets. 4 Since sulphotransferase activity in platelets is well-expressed at birth and a prenatal development of sulphotransferase has been described in mid-gestational human foetal liver, the newborn should be able to sulphate drugs.