The influence of 10−10–10−6 M morphine on the release of [3H]arachidonic acid and its metabolites ([3H]AAM) from prelabeled resident peritoneal murine macrophages was investigated. Morphine enhanced [3H]AAM release from A23187‐ and LPS‐stimulated macrophages, as well as the basal release of [3H]AAM. Dose‐response curves showed a maximum at 10−8 M morphine. Naloxone had no effect on morphine enhancement of [3H]AAM release. These results are in agreement with the hypothesis that [3H]AAM may be involved in the effects of morphine.