Salicylazosulfapyridine (SASP) is a drug used in the treatment of ulcerative colitis (UC) owing to the therapeutic action of the 5-aminosalicylic acid produced by the splitting of the molecule in the cecum, which also yields the absorbable compound Sulphapyridine (SP). The aim of our work was to assess the levels of the drug in blood (SASP and SP), to correlate them with undesirable effects in any, to verify their fluctuations in the dosing interval and to investigate the extent of the excretion of the drug in the children who were studied. 10 children (6 to 16 years) with UC, who were treated with SASP (dOsage schedule 0.5-2.0 g/day in a 12 hours interval), were studied. Blood levels of SASP and SP were assessed at 6 and 12 hours after doses, and total fecal excretion of SASP was determines in 24 hs specimens. All the determinations were performed according to Hansson and Sandberg. SP plasma levels were 17.7 +/- 9.0 ug/ml (range 6.8-36.3 ug/ml) at 6 hours after doses. and 14.1 +/- 7.2 ug/ml (range 5.7-25.0 ug/ml) at 12 hours after doses. SASP plasma levels were 15.5 +/- 15.4 ug/ml (range 2.1-53.4 ug/ml) at 6 hours after doses, and 14.0 +/- 20.4 ug/ml (range 3.9-70.7 ug/ml) at 12 hours after doses. The 24 hours fecal excretion was 17.4 to 236 mg. These values were correlated with the given doses (r = 0.88) calculated as SASP g/m2 body surface 24 hs. There was no statistical correlation between doses and SP or SASP levels in this group, and the respective levels of SASP and SP at 6 and 12 hours after doses showed no significative differences.(ABSTRACT TRUNCATED AT 250 WORDS)