The serological diagnosis of connective tissue diseases (CTDs) is based on the analysis of circulating autoantibodies to cytoplasmic and nuclear proteins (extractable nuclear antigens [ENAs]). The determination of autoantibody specificities supports the clinical diagnosis of the type of CTD and also often the prognosis of the disease. The former indirect immunofluorescence (IIF) technique still provides a useful screening method that currently is supplemented by a range of different techniques allowing the exact determination of single autoantibody specificities. These ENA profiling techniques include ELISA, immunoblotting, line-blot assays, and flow cytometric bead-based multiplex assays. The novel line immunoassay (LIA) from Mikrogen has been introduced in a recent study as a suitable technique for the simultaneous detection of autoantibodies in a routine clinical laboratory, providing comparable results as ELISA and ELiA (both from Pharmacia Diagnostics) (see Damoiseaux et al., this volume). In this study, LIAs from three different manufacturers were performed in 30 serum samples from patients with dermatological manifestations and 27 samples from SLE patients with renal involvement. The line assays from Mikrogen (recomLine ANA/ENA), Innogenetics (Inno-Lia ANA Update), and Imtec (ANA-LIA) were compared for antigen composition, handling, and statistical analysis including sensitivity and concordance. Autoantibody frequencies detected by the Mikrogen, Innogenetics, and Imtec line assays were 14.0%, 19.3%, and 15.8% for RNP; 14.0%, 22.8%, and 14.0% for Sm; 26.3%, 31.6%, and 40.3% for SSA; 3.5%, 12.3%, and 14.0% for SSB; and 3.5%, 14.0%, and 10.5% for histones. Our studies show that the line assay format is an easy-to-use, sensitive, and specific method for ENA antibody detection in human sera.