The stability of propofol in three parenteral nutrient (PN) solutions was studied. Nine combinations of three PN solutions (with amino acid concentrations of 1.5, 2.5, and 5.0%) and three propofol concentrations (0.5, 2.0, and 3.0 mg/mL) were prepared in triplicate and stored at 22 degrees C under fluorescent light. Duplicate samples were visually inspected for color changes, precipitation, or gas formation, and the pH of the samples was determined. These samples were evaluated for propofol content by high-performance liquid chromatography at zero, one, three, and five hours. The stability of the vehicle for propofol injection (similar in composition to fat emulsion) was evaluated by visual inspection, pH determination, and particle-size measurements at zero, one, three, and five hours. The concentration of propofol in all of the propofol-PN combinations remained greater than 90% of the initial concentration except for the combination of propofol 0.5 mg/mL and the 1.5% amino acid PN solution, which contained only 72% of the initial propofol concentration five hours after the start of the study. Visual examination revealed no evidence of color change, precipitation, gas formation, creaming, or streaking in any of the propofol-PN solution combinations. No substantial changes in pH occurred. The particle size of the vehicle for propofol remained relatively constant throughout the study period. Propofol 2 and 3 mg/mL was stable for five hours during simulated Y-site injection with PN solutions containing 1.5, 2.5, and 5% amino acids. Propofol 0.5 mg/mL was stable during simulated Y-site injection with the same PN nutrition solutions for five hours, except for the solution containing 1.5% amino acid.