The prevalence of rheumatoid arthritis (RA) was studied among 266 atopic patients attending an allergy clinic. Two patients had definite RA, a prevalence similar to that seen in the general population. We also studied the prevalence of atopy (positive skin-prick tests) and diseases associated with atopy among forty patients with RA and forty age- and sex-matched controls. The two groups had a similar prevalence of atopy (5 RA patients, nine controls) and atopic diseases (fourteen RA patients, fourteen controls) and they did not differ with respect to blood eosinophil counts or total serum IgE. Positive RAST tests to inhaled allergens were found in three RA patients and five controls and all patients had negative RAST tests to milk and egg. It was concluded that patients with rheumatoid arthritis have a normal prevalence of atopy and atopic diseases and we found no evidence that allergic factors contributed to the arthritis of the forty RA patients in the study.