Methods for improving the fertilizing potential of the spermatozoa in human in-vitro fertilization (IVF) include the stimulation of sperm function in vitro. Metabolic stimulation in vitro has become a major issue in assisted reproductive technology (ART). Here, we review our research on the unselective use of pentoxifylline in IVF for male-factor infertility. Data from our controlled studies indicate that an indiscriminate use of 3.6 mM pentoxifylline, alone or in combination with 3.0 mM 2-deoxyadenosine, is not beneficial in enhancing fertilization rates in zero and poor in-vitro fertilizers or in the presence of antisperm antibodies. An assessment of the effects of pentoxifylline on sperm function prior to IVF may ensure a more rational use of these compounds in selected cases undergoing ART. At present, however, controlled studies in subgroups of patients selected by functional testing are still lacking.