Rheumatoid factor titer was determined on 655 newly admitted mental patients, of whom 32.4% were found positive. When the overall findings were divided into “winter readings” obtained from October through March, and “summer readings” obtained from April through September, the prevalence of positive titers in negro and non‐negro males was found to be significantly higher in the former than in the latter. No such seasonal variations were observed in the corresponding female cohorts.