Expulsive medical therapy of ureteral stones is not well established. To test the efficacy of a calcium antagonist (nifedipine) associated with a corticosteroid (methylprednisolone) in facilitating ureteral stone passage, we studied 86 patients with a unilateral ureteral radiopaque stone not larger than 15 mm. in maximum diameter, confirmed in each case by drop excretory urography. Patients were randomly treated for a maximum of 45 days under double-blind conditions with 16 mg. methylprednisolone plus 40 mg. nifedipine daily (group 1-13 women and 30 men, mean age 45 +/- 14 years, standard deviation) and with 16 mg. methylprednisolone plus placebo daily (group 2-18 women and 25 men, mean age 43 +/- 14 years). All patients also received 2 l. of low mineral content water daily. The average maximum diameter of the stones was 6.7 +/- 3.0 mm. in group 1 and 6.8 +/- 2.9 mm. in group 2 (not significant). Partial ureteral obstruction was present in approximately half of the patients in both groups. Four patients in group 1 and 6 in group 2 dropped out of the study. In group 1, 34 patients had successful results (stone passage without surgical manipulation) and 5 failed (success rate 87%), compared to 24 and 13, respectively, in group 2 (success rate 65%). This difference was significant (p = 0.021, Fisher's exact test). No difference was present in the maximum stone diameter among the successful cases in groups 1 and 2 (6.4 +/- 2.8 and 5.3 +/- 2.2 mm., respectively, not significant). In both groups the maximum diameter of the stone was larger in the failed than in the successful cases (group 1-10.4 +/- 3.0 versus 6.4 +/- 2.8 mm., p = 0.005, and group 2-9.3 +/- 2.5 versus 5.3 +/- 2.2 mm., p = 0.0001). In group 1 the mean interval for stone passage in the successful cases was 11.2 +/- 7.5 days, compared to 16.4 +/- 11.0 days in group 2 (p = 0.036, Student's t test). We conclude that nifedipine associated with methylprednisolone is effective in facilitating ureteral stone passage.