This communication describes the preparation of antibodies to human interleukin 2 (IL-2), using as immunogens synthetic peptides derived from the predicted amino acid sequence of IL-2. Rabbits and mice were immunized with protein carrier conjugates of eight chemically synthesized IL-2-derived peptides, each consisting of 13-15 amino acids. The immune antisera were screened in a solid-phase ELISA for reactivity to a native human IL-2. Antibodies to four of the eight peptides were found by a variety of biological and immuno-chemical criteria to react against human IL-2. Furthermore, an affinity-purified antibody to one of the IL-2 peptides (peptide 84) specifically stained the cytoplasm of phytohemagglutinin-stimulated human peripheral blood lymphocytes or T-leukemic cells (Jurkat). Antibodies to synthetic IL-2 peptides should serve as useful probes for studying this lymphokine and for developing quantitative assays for measuring its levels in biological fluids and its association with disease.