Circulating immune-complexes (CIC) have been detected in sera of vasectomized subjects using the Clq Binding Assay. Results seem to indicate that CIC are a feature of the early post-operative period and a consequence of acute immunization against sperm antigens. The progressive disappearance of CIC from the third month after vasectomy with the simultaneous increase in antisperm antibody percentage and titre suggests that CIC could be a temporary feature in vasectomized men and do not lead to a chronic disease, related to a Type III immune reaction.