The time course of extravascular albumin accumulation responses elicited by the leukotrienes LTC4, LTD4, LTE4, and histamine in the skin were compared in the conscious guinea pig. During the initial 15-min period, comparison of the dose-response curves revealed that histamine produced a much larger increase in extravascular albumin content than any of the leukotrienes. One hour after intradermal injection and at subsequent time intervals, the response to LTD4 had increased in magnitude so that it equaled the response produced by histamine. This was apparent from comparison of the time courses of extravascular albumin accumulation for intermediate doses of LTD4 and histamine and also from comparison of dose-response relationships at 4 h post intradermal injection. In contrast to LTD4, the magnitude of the microvascular permeability responses to LTC4 and LTE4 remained relatively small even over an extended time scale. Although histamine produced a large initial response, this also remained essentially unchanged over a 4-h period. It appears that LTD4 may produce a unique, time-dependent cutaneous microvascular permeability response and measurements over 15-30-min periods may underestimate its activity as a vasopermeability factor. The time-dependent effects of LTD4 on albumin extravasation cannot be ascribed to leukocyte infiltration into the skin since LTC4, LTD4, and LTE4 were entirely without effect in this regard.