Natural killer cells have been shown to interact with MHC class I molecules via inhibitory receptors. However, it is not known whether the inhibition induced by MHC class I molecules requires other NK cell‐target cell interactions. Thus, we examined whether purified MHC class I molecules alone were able to inhibit NK cell function. Purified H‐2K^b and H‐2D^b molecules inhibited the release of IFN‐γ from spleen (H‐2^b)‐derived lymphokine‐activated killer (LAK) cell cultures stimulated by anti‐NK1.1 antibody in a concentration‐dependent manner. LAK cells generated from newborn mice that express low levels of MHC class I binding Ly49 inhibitory receptors were significantly less sensitive to inhibition by H‐2K^b compared to LAK cells from adult mice. Furthermore, LAK cells generated from spleen cells of Ly49C‐transgenic mice were significantly more sensitive to inhibition by H‐2K^b compared to non‐transgenic littermates. Taken together, the data indicate that MHC class I induced inhibition of NK cell mediated effector functions, as assessed by IFN‐γ release after NK1.1 triggering, does not require additional cell surface molecules other than MHC class I.