A new, simplified assay for detecting double stranded DNA antibodies by indirect immunofluorescence using fixed human metaphase chromosomes as substrate is described. The technique has the advantage of ease of preparation, clarity of reading, specificity for double stranded DNA and apparently greater sensitivity than immunofluorescent assays currently available. Thirty of 92 systemic lupus erythematosus sera were found to have double stranded DNA antibodies using the metaphase preparation, compared with 23 positive sera detected with the Crithidia luciliae technique. No double stranded DNA antibodies were detected in 90 sera from patients with rheumatoid arthritis. The human metaphase chromosome assay could replace existing techniques for identification of double stranded DNA antibodies.