The compatibility of paraldehyde with plastic syringes and needle hubs was evaluated. Paraldehyde, USP, was stored in three types of 5-ml syringes: Plastipak, Glaspak, and all glass; the latter type served as the control. At specified times up to 24 hours, the contents of the syringes was evaporated to constant weight, and the residue was weighed. To evaluate the effect of paraldehyde on plastic needle hubs, needles with plastic and metal hubs were immersed in paraldehyde for 24 hours, and the paraldehyde was evaporated. No measurable change in residue weight was noted in any syringes for up to three hours. Compared with the control, there was a significant increase in the average weight of residue in the Glaspak and in the Plastipak syringes at 6, 12, and 24 hours. There was no significant difference in the weight of residue between the Glaspak and Plastipak syringes at those times, however. The amount of residue for the plastic and metal needle hubs was not significantly different. The source of the extractive residue appeared to be the rubber plunger tip. Since the nature of the extractive material in the residue is not known, paraldehyde should be administered in all-glass syringes if possible; other syringe types can be used only if the drug is administered immediately. The use of needles with plastic hubs is acceptable.