A single-blind, randomized clinical trial was carried out to compare the analgesic effectiveness in patients with renal colic of single intramuscular doses of diclofenac sodium (75 mg) versus a dipyrone (1 g)/spasmolytics combination, and diclofenac sodium (75 mg) versus pethidine (75 mg). The first study involved three centres, the second study one centre. In total, 107 patients were treated with diclofenac sodium, 85 with dipyrone/spasmolytics, and 25 with pethidine. Assessments were made during the first hour after drug administration of the degree of pain relief, the severity of pain using a visual analogue scale, and the duration of analgesia. A global assessment of treatment efficacy was made by the participating physicians at the end of the study period. Patients treated with diclofenac sodium showed an earlier onset of analgesia and a higher incidence of total pain relief compared to those treated with dipyrone/spasmolytics or pethidine. Although the mean duration of analgesia was only slightly greater in the diclofenac sodium group than in the dipyrone/spasmolytics group, a significantly longer effect was seen when diclofenac sodium was compared with pethidine (p less than 0.01). Pain severity assessments revealed that diclofenac sodium caused a significantly greater improvement in pain after 60 minutes compared to dipyrone/spasmolytics (p less than 0.05) and after 30 minutes compared to pethidine (p less than 0.05). Global efficacy assessments by the physician rated diclofenac sodium as significantly superior to dipyrone/spasmolytics (p less than 0.01) and pethidine (p less than 0.001). Moreover, diclofenac sodium was better tolerated than either of the comparative treatments. The results indicate that intramuscular diclofenac sodium is a useful alternative to the drugs commonly used in India in the treatment of renal colic.