Objective: To purify the natural antikeratin autoantibody (AK auto-Ab) and observe its effects on the prolif eration of the cultured keratinocytes. Methods: Natural AK auto-Ab was purified by using keratin affinity column, and then the titre and specificity of the Abs were studied by ELISA, immunoperoxidase staining and immuno-electronicmicroscope. The effect of the purified Abs on the cultured keratino-cytes was assayed by 3H-TdR incorporation. Results: Natural AK auto-Ab was obtained. The binding activity of IgG AK auto-Ab in purified Ah remained similar to that in pooled human sera. and the specificity of the obtained antibody is strong. The purified antibody could decrease the Il-TdR incorporation of the cultured keratinocytes in a dose-dependent manner. Conclusion: The method of punning AK auto-Ab is simple, practicable and reliable. Natural AK auto-Ab, existing in normal human individuals, has inhibitory etiect on the proliferation of the cultured keratinocytes. Objective: To purify the natural antikeratin autoantibody (AK auto-Ab) and observe its effects on the prolifration of the cultured keratinocytes. Methods: Natural AK auto-Ab was purified by using keratin affinity column, and then the titre and specificity of the Abs were studied by ELISA, immunoperoxidase staining and immuno-electronic microscopy. The effect of the purified Abs on the cultured keratino-cytes was assayed by 3H-TdR incorporation. Results: Natural AK auto-Ab was obtained. The binding activity of IgG AK auto -Ab in purified Aharently similar to that in pooled human sera. And the specificity of the obtained antibody is strong. The purified antibody could decrease the Il-TdR incorporation of the cultured keratinocytes in a dose- dependent manner. Conclusion: The method of punning AK auto-Ab is simple, practicable and reliable. Natural AK auto-Ab, existing in normal human individuals, has inhibitory etiect on the proliferation of the cultured keratinocytes.