In eleven pregnant patients with ulcerative colitis or Crohn's disease who were treated with sulphasalazine (SASP) the serum concentrations of SASP and sulphapyridine (SP) were measured at delivery. The concentrations of SASP and SP were almost identical in the cord serum and the maternal serum. In seven of the women the same concentrations were measured at a later occasion when they were not pregnant. The serum SASP concentration remained the same, but the SP concentration was higher in the non-pregnant women. This probably reflects the different degree of protein binding of SASP and SP, respectively, and the change of distribution volume that occurs in pregnancy. In the newborn the concentrations of SASP and SP were 4.6 +/- 3.1 microgram/ml and 18.2 +/- 8.7 microgram/ml, respectively. Current studies have shown that neither SASP nor SP in these concentrations causes significant displacement of bilirubin from albumin. Thus, SASP can be given to the pregnant patient up to delivery without risks for the newborn full-term infant.