Abstract: The cyclic AMP and the cyclic GMP in the sera were assayed from fifty one patients with psoriasis. The cyclic AMP was determined by competitive protein-binding method and the cyclic GMP by radioimmunoassay.The values of the cyclic AMP hail no difference (P>0.05) and the values of the cyclic GMP were significantly different (P<0.01) between the normal individuals and the psoriatic patients. The ratio of the cyclic AMP and the cyclic GMP was 1.71 in the normal individuals and 1.02 in the psoriatic patients.The extent of the eruptions was not related to the level of cyclic AMP and was closely related to the level of cyclic GMP.The values of cyclic A1V1P were of no statisticf difference and the values of cyclic GMP were significantly different between the progressive stage and the static stage of the patients. Cytotoxic drugs might obviously reduce the level of cyclic GMP in the sera and gave no effect to cyclic AMP.The authors also discussed the mechanism through which cyclic nucleotides participated in the regulation and the control of proliferation and differentiation of the epitlielial cells.