["To investigate whether Kremer's sperm-mucus penetration test may predict sperm fertilizing ability in IVF.", "Kremer's test was prospectively performed on semen samples used for 66 consecutive IVF trials and compared with the fertilization rates and fertilization failure rates observed.", "Fertilization rates were significantly reduced in cases of abnormal Kremer's test (42% versus 51%; n = 745 oocytes with a statistically insignificant increase in fertilization failure rates (21% versus 10%; n = 66 trials). For abnormal semen, fertilization rates (39% versus 39%; n = 208 oocytes) and fertilization failure rates (20% versus 28%; n = 17 trials) were similar regardless of Kremer's test result. For normal semen, an abnormal Kremer's test implied a significant decrease in fertilization rates (44% versus 54%; n = 537 oocytes) with a statistically insignificant increase in fertilization failure rates (21% versus 6%; n = 49 trials)."] Does abnormal sperm-mucus penetration test predict low in vitro fertilization ability of apparently normal semen?