patients, whereas polymyositis, esophageal dysmotility, and scleroderma were found mainly in MCTD patients. In one sample (obtained from a SLE patient), no antibodies to recombinant protein A, protein C, and the 70 kD protein could be identified. In this patient, anti-RNP antibodies were revealed only when a purified antigen was used.Antibodies to (a) RNP-A, RNP-C, and RNP-70 kD; (b) RNP-A and RNP-70 kD; (c) RNP-A and RNP-C; (d) RNP-C and RNP-70 kD; (e) RNP-A only; (f) RNP-C only; and (g) RNP-70 kD only were found in, respectively, 9, 0, 3, 1, 0, 0, and 0 of the 14 SLE patients and in 13, 2, 2, 1, 0, 0, and 2 of the 20 MCTD patients. These distributions were comparable in SLE and MCTD. The patients with chronic idiopathic urticaria, rheumatoid arthritis, or parotitis had antibodies to, respectively, RNP-70 kD only, RNP-A and RNP-C, and RNP-70 kD only. Table 1 contains a survey of