Over an 11-year period in Edinburgh, 495 patients with a proven diagnosis of testicular torsion or acute epididymo-orchitis were admitted to hospital. The final diagnosis in 227 was epididymitis, in 236 torsion of the testis and in 32 torsion of a testicular appendage. The immediate salvage rate from torsion of the testis was 67 per cent. To try to improve diagnostic accuracy in these three conditions, a computer program was constructed using a data base derived from the literature. On retrospective analysis of the 495 patients, the program achieved a 92.3 per cent accuracy in differentiating torsion from epididymitis. If the computer's diagnosis had been followed it would have reduced the exploration rate in epididymitis from 18 to 1.8 per cent. It would further have increased the diagnostic accuracy of a junior doctor to that of a senior colleague, but the number of torsions 'missed' by the computer and senior doctor would have been similar. The technique is inexpensive, rapid, immediately available, non-invasive and easy to use. It is suggested that such a program will increase diagnostic accuracy in acute testicular pain and, hopefully, the salvage rate from torsion of the testis.