Hypo-osmotic swelling test: analysis of prevasectomy ejaculates.

The hypo-osmotic swelling (HOS) test was applied to 1,890 ejaculates obtained from previously fertile men who subsequently underwent a vasectomy. Less than 3% of the ejaculates produced an abnormal HOS test (less than 50% swelling), and more than 95% were normal (greater than or equal to 60% swelling). The sperm concentration and motility data were similar to those obtained by other investigators with prevasectomy ejaculates. Statistically significant but low correlation coefficients were present between the HOS test and these other sperm variables. On the assumption that the large majority of these men were fertile when the ejaculates were produced, the results support the contention that fertility is usually associated with normal or, occasionally, equivocal values in the HOS test.