Fifty sera containing antinucleolar antibodies were o gathered in a routine laboratory during testing for antinuclear antibodies with indirect immun-fluorescence over a five-year period. The patients involved were suffering from sclerodermia (13 cases), rheumatoid arthritis (7 cases), polymyositis (3 cases), lupus (2 cases), various rhumatismal disease (59 cases) and non rhumatismal diseases in 16 cases, including 5 malignant diseases. In 80 per cent of the cases nucleolar fluorescence was combined with nuclear fluorescence of another type. The antibodies were almost always of the IgG category and belonged in 2/3 of cases to several immunoglobulin categories, most often IgG-IgA. Pretreatment of the liver cuttings with RNase always modifies the nucleolar fluorescence, most often making it negative, and pretreatment with DNase using a combination of enzymes 10 times higher also modifies it (more often decreasing it than making it negative), which indicates that the nucleolar antigen, probably an ARN with a low molecular weight, also depends upon the ADN.