In order to evaluate the efficacy of oral administration of a pharmacological dose of folic or of folinic acid to prevent the folate deficiency in patients with inflammatory bowel disease (IBD) treated with salicylazosulfapyridine (SASP) (1g twice daily at meal times), two groups of 15 patients with IBD received 15 mg/day of folic or folinic acid for one month. In both the groups there were ten patients affected by Crohn's disease and five patients affected by ulcerative colitis. Before starting the treatment, the plasma folate and the red blood cell (RBC) folate concentrations did not statistically differ between the two groups. After one month the mean increase in RBC folate concentration was significantly greater after folinic therapy then after folic acid therapy (910 +/- 383 versus 570 +/- 212 ng/ml; p less than 0.01), while no difference was observed in the mean increase of plasma folate level (19.8 +/- 6.6 versus 18.5 +/- 5.0 ng/ml). It was concluded that: a) both folic and folinic acid could restore and enlarge the body stores of folate in patients with IBD treated with SASP, when administered at the dose of 15 mg daily for one month; b) folinic acid seems to be more efficient in enlarging the body stores of the vitamin than folic acid.