Distribution of viral antibodies was examined by the indirect fluorescent antibody technique in specimens from rheumatoid arthritis and from systemic lupus erythematosus patients. Titres in sera from rheumatoid arthritis patients were usually equal to, or greater than, those in joint fluids. Viral antibodies were found in whole cryoprecipitates from joint fluids and in the IgG fractions of the cryoprecipitates. Anti-herpes simplex antibodies were most frequently found in cryoprecipitates and were at highest titre in sera and joint fluids. Anti-respiratory syncytial virus antibodies were next in frequency and in titre. No evidence was presented to support the concept of localized viral antibody synthesis in joints of rheumatoid arthritis patients. Serum antibody titres in systemic lupus erythematosus patients were similar to those in rheumatoid arthritis patients; however, viral antibodies were not found in the serum cryoprecipitates of systemic lupus erythematosus patients.