In this report, we present data on the expression and function of Fc gamma RII (CD32) by natural killer (NK) cells. Highly enriched NK cell populations were isolated from peripheral blood lymphocytes by negative selection and consisted of > or = 95% CD3-/CD56+ cells. Flow cytometric analyses with anti-CD32 monoclonal antibodies (mAbs) demonstrated that a small proportion of NK cells were recognized by mAbs IV.3 and 41H16. Two-color flow cytometric analysis indicated coexpression of the epitope on NK cells recognized by both these mAbs. Verification of expression of CD32 on NK cells was obtained by demonstrating coexpression of CD32 on either CD16+ or CD56+ cells. The CD32+/CD16+ and CD32+/CD56+ cells represented approximately 7 and 3% of the total, respectively. CD32 transcripts were identified from highly purified NK cells using reverse transcription-polymerase chain reaction with CD32-specific primers, followed by Southern blotting. Enhanced chemiluminescence-Western blot (ECL-WB) analysis of lysates of purified NK cells indicated that mAb IV.3 recognized a molecule of approximately 40 kD. The Fc gamma RII on NK cells was able to transduce intracellular signals in several types of assay. Cross-linking of anti-CD32 resulted in a mobilization of intracellular Ca2+, although to a lesser extent than that induced by cross-linking CD16. Both mAbs IV.3 and 41H16 were found to be capable of inducing reverse antibody-dependent cellular cytotoxicity against FcR+ target cells (e.g. P815). These data represent the first direct description of the expression and function of Fc gamma RII on human NK cells.