Tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and granulocyte monocyte-colony stimulating factor (GM-CSF) were measured in serum and involved and uninvolved skin blister fluids of 20 psoriatic patients and 10 healthy subjects, by enzyme immunoassay. TNF-alpha and IL-6 were always detectable in involved skin blister fluids, while GM-CSF was detected only in 45% of these samples. TNF-alpha, IL-6 and GM-CSF were detected in 95, 100 and 10% of uninvolved skin blister fluid samples, respectively. TNF-alpha and IL-6 were found in 50 and 30% of control blister fluids, while GM-CSF was never detected. In serum, TNF-alpha was detected in 75% of patients and in 70% of controls; IL-6 in 45% of patients and in no controls; and GM-CSF in 35% of patients and in 20% of the controls. The median TNF-alpha and IL-6 levels in involved skin were statistically higher than those of both uninvolved and control skin blister fluids. TNF-alpha and IL-6 levels in blister fluids obtained from both involved and uninvolved skin were higher than those of the patients' sera. GM-CSF, when present in involved skin blister fluids, showed correlated levels with the other cytokines (TNF-alpha: R = 0.85, P = 0.004; IL-6: R = 0.72, P = 0.03). TNF-alpha was highly correlated with IL-6 (R = 0.78, P < 0.00001) in involved skin blister fluids. TNF-alpha and IL-6 levels of involved skin blister fluids showed significant correlations with the psoriasis area and severity index scores in the patients, suggesting a direct relationship between these cytokines and the clinical manifestations of the disease. Moreover, the TNF-alpha levels were particularly related to the erythema scores in the patients, further supporting evidence of their role in the pathogenesis of the disease.