Synovial fluid from the knee joints of 20 psoriatic arthritis patients (8 with polyarthritis and 12 with mono / oligoarthritis) were studied to de¬tect the value of interleuldn-1 beta. ESR and serum C-reactive protein were also measured. Quantitative immunoassay method showed a signif¬icant increase of interleukin-1 beta in the synovial fluid of polyarthritis group as compared to mono/oligoarthritis group, while, ESR. C-reactive protein and synovial flwd total protein, acid phosphatase and WBCs shou»ed non significant changes between the two groups. So, the synovial fluid interleukin-1 beta is one of the parameters which differentiate be¬tween the two groups. Synovial fluid interleukin-1 beta showed signifi¬cant correlation with the number of affected joints and joint score and non-significant correlation with ESR and C-reactive protein. Results con-firm the role of interleukin-1 beta in the pathogenesis of psoriatic arthritis as well as to select those who will be in need for aggressive and non con¬ventional treatment.