Received April 28, 1998
Accepted May 17, 1998

Introduction: The aim of this study is to determine the suitability of the hypo-osmotic sweIling test (HOS) in identifying viable spermatozoa in fresh and frozen-thawed samples for intracytoplasmatic sperm injection (lCSI). Materiais and Methods: Semen specimens were obtained from 11 normozoospermic men according to the WHO criteria. A 100 µ1-aliquot of each specimen was removed and subjected to hypo osmotic swelling in a fructose and sodium citrate solution and to Hoescht-33258 to assess viability. The specimens were then diluted with glycerol TEST-yolk buffer (Irvine Scientific, Santa Ana, California) (1:1, v/v) and cryopreserved by the liquid nitogen vapor method. After thawing and removal of the cryomedia, the specimens were again submitted to hypoosmotic sweIling and to Hoescht-33258 to assess viability. A fluorescence microscope equipped with contrast fase was used to assess viability by Hoescht in the same ceIl either before and after cryopreservation. Eosin-nigrosin supra-vital staining (EN) was used to validity the Hoescht viabiIity results. Results: A high positive correlation was seen between the presence of sperm swelling by HOS and viability by Hoescht 33258 before freezing (r=0.95, P=0.000I ). After cryopreservation, a poor correlation was seen between HOS scores and Hoescht-33258. Hoescht-33258 viability results were validates by EN staining (r=0.72, P<0.0004). Conclusion: The hypo-osmotic swelling test is a simple, functional and non-deleterious assay that can accurately detect viable spermatozoa for ICSI in fresh human sperm. However, this test may not be clinically helpful in the selection of viable ceIls in cryopreserved samples.