In a series of 163 patients with systemic lupus erythematosus (SLE) and/or systemic sclerosis and/or mixed connective tissue disease (MCTD), the presence of antibodies to a 68 kDa U1RNP associated polypeptide was more predictive for SLE (88%) than for MCTD (38-68%) using 3 different sets of proposed criteria for the latter condition. In all but one case studied serially the immunoblotting profile remained constant. In SLE recognition of the 68 kDa polypeptide identified a subset with increased vasoreactivity with Raynaud's phenomenon (96%, p less than 0.001) and swollen fingers (68%, p less than 0.001) whereas recognition of a 47 kDa La (SSB) polypeptide was associated with photosensitivity (72%, p less than 0.02), less renal involvement (p less than 0.05) and an older age of disease onset (46.6 years +/- 18.3 SD, p less than 0.002).