Postpubertal mumps may result in ochitis and permanent testicular atrophy may develop following infection. This present study was initiated to evaluate the preventive effect of interferon-alpha2B on infertilty after mumps orchitis. There were 21 patients with mumps orchitis between May 1990 and June 1997. Patients were randomly distributed into 2 groups: group 1 patients (n=13) maintained therapy with interferon-alpha2B (3x10(6) IU per day) and group 2 were managed by conservatively. All of the patients were evaluated with testis size measurement, mumps virus titer, hormone level, and if possible semen analysis. For group 1 patients symptoms disappeared within 2 to 3 days and the volume of testis returned to normal within 11 days and testis atrophy was not observed in all patients in follow up. But asthenospermia was continued in 4 patients (unilateral 2, bilateral 2). For group 2 patients symptoms disappeared within 5 to 6 days and the volume of testis returned to normal within 10 days and testis atrophy was observed in 3 patients (unilateral 2, bilateral 1) in floow up. Asthenospermia was continued in 4 patients (unilateral 2, bilateral 2). Sperm count and morphology were recovered all the recover in group 1, 4 patients had persistent reduced sperm count and morphology in group 2, respectively. These observations suggest that systemic interferon-alpha2B treatment is highly effective in preventing infertility as well as testicular atrophy after mumps orchitis.