The Lewis group system is intricately related to the secretor system, which in turn controls the presence of ABH factors in human secretions. It has been suggested that Lewis typing of secretion stains could help to verify non-secretor results obtained in ABO typing; however, the literature contains conflicting reports on the presence of Lewis substances in secretions. As a preliminary study in the investigation into the usefulness of Lewis typing in case-work, we examined paired saliva and vaginal stains and paired saliva and semen stains from laboratory donors. The activity of Lewis substances per se in these secretions and their viability in stains over a ten-week period are described.