Cultured mouse melanoma cells were removed from incubation to room temperature and injected with either 1 μM of morphine or its mu-receptor antagonist naloxone, or, not treated. Photon emissions were counted measured by a photomultiplier unit for 24 hr. Cells injected with morphine exhibited conspicuous bursts of photon emissions whose amplitudes were as much as 1000 times greater than naloxone-injected or non-treated comparison cells with durations of about 10 s for about one hour. The peaks of the photon bursts in cells injected with morphine were approximately 10-11 W•m-2 and could involve the synchronized release of energy from all or most of the million cells in the population. The average photon emissions for these cells remained 6 fold greater for 24 hrs. If the multiple spikes and maintained elevation of photon emissions from the morphine-injected but not naloxone-injected or non-treated cells comprise a form of inter-cell communication this phenomenon may partially explain the propensity for morphine treatment to elicit proliferation and metastases in some malignant environments.