A reversed-phase ion-pair HPLC assay has been developed for quantitating morphine, codeine, apomorphine, and pseudomorphine in aqueous solutions. Using two types of plastic syringes, the effect of light (25 W) and temperature (22 and 3 degrees C) on the stability of morphine, over a 12-week period, has been investigated in the presence and absence of preservative and antioxidant. The leaching of contaminants from the plastic syringes to water stored in them, for a period of up to 12 weeks, has also been investigated. The results indicate that less than 3% of the morphine is degraded in both types of plastic syringes, stored in light at 22 +/- 2 degrees C. The degradation is even less prominent in the dark or at 3 degrees C. Pseudomorphine has been identified as the major degradation product. Using 5% degradation of drug as the criterion for the determination of the shelf-life of morphine, it was found that in one brand of plastic syringes, morphine has a shelf-life of the order of 20 and 33 weeks, in the absence and presence of preservative and antioxidant, respectively. In the other brand of plastic syringe, the drug has a shelf-life of greater than 1 year. Some unidentified leached contaminants have been detected in water stored in both brands of syringes.