The present investigation was undertaken to study the potential role of extracellular calcium on the release of arachidonic acid from mouse peritoneal macrophages. Both in phorbol ester-treated and in Ca2(+)-depleted cells, a rapid release of arachidonic acid was seen in direct response to added Ca2+. The response was directly dependent on the extracellular Ca2+ concentration, with a Ca2+ threshold of 100 nM. These results support the notion that arachidonic acid release in macrophages is functionally coupled to influx of external calcium.