Abstract: The serum total nucleic acid, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) concentrations detected in 105 patients with psoriasis of different stages are reported in this paper. The serum total nucleic acid, DNA and RNA concentrations in the patients were all markedly lower than those of normal control group (P<0.001-0.05). The serum total nucleic acid, DNA and RNA concentrations in progressive and stationary stages were lower than those in resolving stage (P<0.01-0.02). Total nucleic acid, DNA and RNA concentrations in resolving stage mostly returned to normal value. This change of serum concentrations paralleled with the increasing activity of ribonucleic (RNase) in serum and urine. The authors consider that the decreasing of nucleic acid concentration may be related to degradation action of RNase. In order to explain the pathogenesis of psoriasis and look for the most effective therapeutic method, it is necessary to study the metabolism of nucleic acid in patients with psoriasis further.