Systemic lupus erythematosus (SLE) may be associated with thrombocytopenia on one hand and lymphoma on the other. Interleukin-3 (IL-3) may contribute to both conditions. IL-3 is a pleotrophic growth factor affecting the proliferation and differentiation of stem cells to committed progenitors of several hematopoietic lineages including megakaryocytes and lymphocytes. The serum level of IL-3 determined by ELISA was found to be higher in a cohort of 16 patients with SLE in comparison to healthy controls. The IL-3 levels were highest in 2 patients with SLE and lymphoma. Interestingly, low serum levels were detected in SLE patients with thrombocytopenia. Our preliminary results may point to the role of IL-3 in the hematopoietic changes observed in SLE.