This paper reviews the work of 11 different in vitro fertilization (IVF) groups from around the world in an effort to determine the effectiveness of IVF as a therapy for male factor infertility as well as threshold values for semen parameters that are synonymous with success. Two key questions that are asked are: 1) What fertilization rate is expected for male factor patients and 2) Can we predict which patients will fertilize. The immediate problem which arises in attempting to compare results from various groups is that there is no standardization in male factor criteria. This lack of agreement in what constitutes an abnormal semen sample is also reflected in the fertilization rates and threshold values. The first group reviewed (Mahadevan, 1983) suggest greater than 20% motile in the initial semen sample as a threshold value required for success while the second group (Cohen, 1985) presents 6 couples with less than 20% motility achieving pregnancy. Such inconsistencies in results are typical of this confusing and controversial area. Fertilization in IVF has been achieved with as few as 2 x 10(6) sperm/ml or as low as only 2% motility in the initial semen sample. It appears that most workers would agree that the lower limits of traditional semen parameters that are compatible with success are not well defined. Consensus might also be reached on the fact that fertilization rates are usually significantly lower in male factor cases than in normal semen parameters coupled with tubal infertility. Beyond those two factors, little agreement is found in the literature. The spectrum of methodology for semen processing is very broad and often not clearly detailed. In addition to the additional semen parameters of count, motility, and morphology, attempts have been made to establish other prognostic tests such as the sperm penetration assay (SPA), acrosome reaction determinations, and motility parameters such as velocity, linearity and lateral head displacement. Controversy abounds concerning the value of these newer tests. Threshold values for acrosome reaction and motility parameters have not been established. The SPA is believed to be highly predictive by some and unreliable by others. The one redeeming feature of this IVF male factor area is that it seems to be one of the most effect treatments for male factor infertility.