A multicenter double-blind study of the effectiveness of sulfasalazine and 6-methylprednisolone, alone and in combination, was conducted on 452 patients with Crohn's disease. One hundred sixty patients were previously untreated; 292 patients were previously treated. The Crohn's disease activity index (CDAI) was used to determine whether a patient had active (CDAI greater than or equal to 150, n = 215) or quiescent disease (CDAI less than 150, n = 237). Treatment of active disease consisted of high-dose 6-methylprednisolone, 6-methylprednisolone combined with 3 g of sulfasalazine, 3 g of sulfasalazine alone, or placebo, and lasted 6 wk. Patients in remission received maintenance doses of one of these drug regimens for periods of up to 2 yr. One hundred ninety-two patients completed the 2-yr study period. Results were evaluated using life-table analysis and outcome ranking. These methods showed 6-methylprednisolone to be the most effective drug in overall comparison of all patients (p less than 0.001); in previously treated patients (p less than 0.001); and in subgroups: active disease (p less than 0.001), only small bowel disease (p less than 0.05), and both small bowel and colon disease (p less than 0.05). Combination of 6-methylprednisolone and sulfasalazine was the most effective regimen in previously untreated patients (p less than 0.05) and when disease was localized in the colon (p less than 0.001). Sulfasalazine alone was least effective in overall comparison of all patients (p less than 0.05) and in all strata. Drug treatment was of no significant benefit to patients with quiescent disease. Continuous administration of low doses of 6-methylprednisolone, or the combination regimen, was beneficial in patients who responded initially to treatment of active disease. The addition of sulfasalazine, however, offered no advantage.