Increased microvascular permeability in vivo in response to intradermal injection of neutrophil-activating protein (NAP-2) in rabbit skin. Neutrophil-activating protein-2 (NAP-2), an NH2-terminally processed form of the platelet-release product beta thromboglobulin (beta TG), was purified to homogeneity from stimulated human blood leukocytes. In the presence of a vasodilator substance (PGE2, CGRP) picomolar (pmol/l) amounts of NAP-2 induced neutrophil accumulation and plasma leakage on intradermal injection in rabbit skin, whereas the longer forms, beta TG itself and connective tissue-activating peptide III (CTAP-III), had no such effect. NAP-2-induced increased in microvascular permeability was neutrophil dependent and fast in onset, with a half-life of 65 to 75 minutes, comparable to that previously reported for the structural-related neutrophil-activating protein-1/interleukin-8 (NAP-1/IL-8). However NAP-2 showed a lower potency in that more protein was needed to provoke skin reactivity. Nevertheless the finding that a platelet release product can elicit neutrophil-mediated inflammation further narrows the gap between thrombotic events and inflammatory disorders. 