The clinical activity of systemic lupus erythematosus (SLE) may be influenced by ethnic and environmental factors. The Consensus group on Activity Criteria for SLE attempted in a multicenter study to determine well-accepted criteria for disease activity. Of the 704 randomly assigned patients, 41 (5.8%) were from Israel. A detailed history including epidemiological, clinical and laboratory data was recorded. Significant differences were found between Israeli and European patients in the occurrence of Raynaud's phenomenon [12 (30%) vs. 358 (51%), respectively (P < 0.05)] and skin vasculitis [6 (15%) vs. 216 (34%), respectively (P < 0.05)]. In addition to those clinical differences, significant differences were also found in the occurrence of VDRL, low complement levels and lupus anticoagulant. Additional differences were found in some laboratory data, indicating differences in the sensitivity of the various laboratories. We conclude that the differences between the Israeli and European groups in the clinical data can be attributed mainly to environmental factors (weather, viruses), and in the laboratory data to ethnic differences (e.g., HLA) and to the different diagnostic methods used.