The authors sought serum antinuclear antibodies by the indirect immunofluorescent method in 3,260 patients, and found these antibodies in 293 of them. 90 patients had a level equal or greater than 1/50. Among the latter, 54 had some form of collagen disease. The following facts are emphasized: -- antinuclear antibodies are always present in lupus erythematosus. Their levels fall under the influence of treatment when nephritis occurs; -- their frequency is greater (13 cases out of 16) during scleroderma, with often a hazy appearance; -- they are lower during rheumatoid arthritis (23% of cases had a significant level), and their presence is not a sign of worse prognosis; -- they were absent in other forms of collagen diseases.