The purpose of this study was to evaluate the clinical usefulness of squamous cell carcinoma antigen (SCC Ag) in patients with squamous cell carcinoma of the larynx. Plasma specimens were obtained from 70 patients with cancer of the larynx before and after treatment and during follow-up. Disease status and the marker levels were determined blind to each other. Microparticle enzyme immunoassay (IMx SCC) was used to measure the SCC Ag level. Applying standard normal limits the sensitivity of the marker at diagnosis was 25.7%. SCC Ag levels were generally lower after therapy than before. Relapse occurred more often in patients with an abnormal pretreatment SCC Ag level, which was more frequent in those with nodal invasion. The marker level increased in 70% of the patients with relapse before the clinical detection of recurrence. SCC Ag is of limited usefulness in the primary diagnosis of cancer of the larynx, but is useful in detecting recurrence of cancer.