The stability of a combination of meperidine hydrochloride 50 mg, promethazine hydrochloride 25 mg, and atropine sulfate 0.4 mg in plastic syringes at room temperature was studied. The samples were tested for each drug after 0.5, 1, 3, 6, and 24 hours in the syringes. Freshly prepared mixtures of the drugs in glass containers were used as controls, and three trials using separate test mixtures were performed. A gas chromatography procedure was used; atropine was separated from the mixture and assayed alone for greater accuracy. Drug concentrations in the plastic syringes were not significantly different from controls at any of the test times. A mixture of meperidine hydrochloride, promethazine hydrochloride, and atropine sulfate in dosages commonly administered as a preoperative medication was stable for 24 hours in plastic syringes.