Objective: To test the hypothesis that α-glycosidase activity in seminal plasma can predict the outcome of both IUI and IVF.Design: A retrospective cohort study.Setting: Tertiary fertility center in a university hospital.Patient(s): Eighty-three subfertile couples who underwent IUI and 125 subfertile couples who underwent IVF.Intervention: None.Main Outcome Measure(s): Determination of the α-glycosidase activity in seminal plasma before an IUI or IVF attempt, correlation of α-glycosidase activity and other semen parameters, and prediction of pregnancy using α-glycosidase activity in seminal plasma.Result(s): α-Glycosidase activity correlated with sperm count. In the IUI group, α-glycosidase activity of >23.9 mU/mL predicted pregnancy with a sensitivity of 100% and a specificity of 55.2%. In the IVF group, the outcome could not be predicted with use of any of the semen parameters.Conclusion(s): α-Glycosidase activity measured in mU/mL probably can be used as a predictor for IVF and pregnancy in an IUI program but has no predictive value with regard to pregnancy rate in an IVF program.