Polymorphonuclear leukocyte (PMN) and monocyte (MN) chemotaxis in nine patients with pustulosis palmo-plantaris (PPP) and ten patients with pustular psoriasis (PP) was determined by an objective in vitro assay employing a 51Cr-labelling technique. PMN chemotaxis was significantly enhanced in both groups of patients compared with controls. MN chemotaxis was normal. There was no difference in the chemotactic responsiveness of leukocytes from patients with PPP and PP. The random migration of PMN and MN from the patients was normal. Homogenized tissue specimens from lesional skin with and without pustules, and from perilesional, normal-looking skin of PPP and PP were analysed for the presence of chemoattractant(s) for PMN. Lesional skin had considerable chemoattractant properties, but perilesional skin did not induce directed migration of PMNs.