Abstract: SPA reagent made from native staphylococcus No:1800 strain labelled with 16 specific antibodies, was used for the co-agglutination test on the sera of certain skin diseases, The authors observed 390 patients, these patients include 82 cases of psoriasis vulgaris, 44 cases of allergic dermatitis, 33 cases of eczema, 47 cases of dermatitis seborrheica, 42 cases of acne vulgaris, 19 cases of urticaria chronica, 18 cases of erythema exudativum, 8 cases of folli culitis, 2 cases of pustulosis palmaris et plantaris. 14 cases of decmatomycosis, 5 cases of tuberculosis cutis,9 cases of alopecia areata, and 3 cases of erysipelas etc.Of these 82 cases of psoriasis, 50 cases showed positive co-agglutination test(69.7%).The test was positive in 18 out of 33 cases with eczema (54.5%), 21 out of 44 cases with allergic dermatitis (47.7%). 8 out of 18 cases with erythema exudativum, The results of 51 normal human sera were all negative. The co-agglutination test of SPA No: 1800 strain labelled by B streptococcus antisera and adenovirus Ⅲ antisera was positive in 30% of cases. The authors suggest that it may play a certain role in the pathogenesis of these dermatoses.