The purpose of this study was to measure soluble CD 14 (sCD14) molecules in the skin and in serum of patients with psoriasis. CD 14 is a newly discovered cell surface marker on monocytes that is shed after cell activation. The following procedures were used: suction blisters were raised over the abdominal skin of 9 healthy control individuals and 8 patients with psoriasis. Serum of 17 healthy controls and 17 patients with psoriasis was collected. sCD14 was determined in suction blister fluid and serum by the ELISA technique. The clinical status of psoriasis was rated by the psoriasis area and severity index (PASI score). We found that sCD14 levels in suction blisters of healthy skin (1,050 ± 236 ng/ml, mean ± SE) were similar to those of nonlesional psoriatic skin (841 ± 113 ng/ml). By contrast, control serum contained 2,687 ± 167 ng/ml, but psoriatic serum 4,059 ± 388 ng/ml sCD14 (p = 0.001, Wilcoxon test). Linear regression analysis revealed that serum sCD14 levels and the PASI score of patients did not correlate. We conclude that there is an abnormal monocyte stimulation in blood but not in nonlesional skin in psoriasis that is independent from the clinical status expressed by the PASI s