The effect of irrigation of vasa deferens on the postvasectomy semen content of 70 men was determined. To avoid recanalization, the cut ends of the vasa were sutured in different fascial planes. In 20 other cases the distal ends of the vasa were also irrigated with 20 cc of the highly acid Kystosol solution before suturing. 2 weeks later only 1 patient sh owed azoospermia after vasectomy alone and only 5 after vasectomy plus t he irrigation. Nonmotile sperm were found in 42 cases among the vasectomy-alone group and in 15 cases in the irrigated group. In the vasectomy-alone group, motile sperm cells were found in 27 patients but no motile sperm cells in the irrigated patients. 2 months after vasectomy absence of spermatozoa was noted in 31 (44%) patients following vasectomy alone and in 18 patients (90%) after added irrigation. In 2 instances, motile cells were still present in vasectomy-alone patients. 3 months' postvasectomy 64 (91%) of the vasectomy-alone group were azoospermic and all of the irrigation group. At 4 months, all except 1 were azoospermic. This patient was later shown to have recanalization of a vas. It is concluded that although irrigation of the vasa deferens with Kystosol solution facilitates the disappearance of sperm cells from ejaculates after vasectomy, 2 totally azoospermic semen analyses are needed to assure sterility.