SOME difficulties in clinical studies of endocrine function based on plasma sampling regimens include time-consuming venipuncture and measurement of the “total” rather than the “free” biologically active fraction in plasma. Simple methods for determining plasma free steroids have not yet been developed, and most current procedures involve technically demanding ultrafiltration or equilibrium dialysis. In this context measurement of steroids in saliva is attractive. Steroid concentrations in saliva are independent of flow rate and reflect those in the free fraction in plasma. Recent improvements in immunoassay techniques have allowed development of simple, high output assays for salivary steroids which are well suited for routine use. Since saliva samples can be collected at frequent intervals by both adults and children, they facilitate short term dynamic tests, pharmacokinetic analyses, and studies of chronobiological changes. Problems of viscosity, which restrict processing of freshly collected saliva, may be resolved by deep-freezing, and storage of samples at −20 C for prolonged periods is acceptable.