This study investigates the effect of pentoxifylline on sperm movement and zona pellucida binding. Spermatozoa from nine teratozoospermic patients (10.2 +/- 6% normal forms) were included in the study. Test samples were diluted with a 4 nM solution of pentoxifylline, and control samples with Ham's F-10 culture medium only. Zona pellucida binding potential was measured under hemizona assay conditions (HZA). Sperm motility was evaluated at the start (0 h post-swim-up) and end (4 h) of the HZA, under test-tube conditions and under HZA conditions (50 microliters droplet under oil). Motility parameters tested included the curvilinear velocity (VCL), straight line velocity (VSL) and linearity (LIN). Compared to the controls, pentoxifylline-treated samples showed an immediate stimulation of sperm motility, under test-tube conditions, with a significant elevation of VCL at 0 h incubation (102.77 +/- 14.4 versus control value 84.60 +/- 10.6 microns/s; P = 0.005), which however was reversed after 4 h incubation (73.16 +/- 4.6 versus control value 85.47 +/- 12.8 microns/s; P < 0.005). A decline in sperm motility from 0 to 4 h incubation was noted for all the pentoxifylline-treated samples, under both test tube conditions (VCL: 102.77 +/- 14.4 versus 73.16 +/- 4.6 microns/s, P < 0.005; VSL: 27.2 +/- 10 versus 10.66 +/- 2.2 microns/s, P < 0.005; LIN: 23.65 +/- 7.1 versus 11.86 +/- 1.8%, P < 0.005) and HZA conditions (VCL: 100.04 +/- 13.1 versus 76.00 +/- 7 microns/s, P < 0.005; VSL: 26.40 +/- 8.7 versus 9.14 +/- 4.5 microns/s, P < 0.005; LIN: 26.2 +/- 12 versus 11.05 +/- 4.3%, P < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)