The physical compatibility of Precedex with 95 other drugs during simulated Y-site injection was evaluated by visual observation, turbidity measurement, and electronic particle content assessment (when appropriate). Five-milliliter samples of Precedex 4 micrograms/mL in 0.9% sodium chloride injection were combined with 5 mL of each of 95 other drugs. The other test drugs included anti-infectives, analgesics, antihistamines, diuretics, steroids, and other supportive-care drugs undiluted or diluted in 0.9% sodium chloride injection or 5% dextrose injection (for amphotericin B). Visual examinations were performed with the unaided eye in normal diffuse fluorescent light and with a Tyndall beam (a high-intensity monodirectional light beam) to enhance the visualization of small particles and low-level turbidity. The turbidity of each sample was measured as well, as was the particle content of samples with no visible incompatibility. Evaluation of the samples was performed initially and at 1 and 4 hours after preparation. Ninety-three of the 95 test drugs were compatible with the Precedex dilution during the 4-hour observation period; however, both amphotericin B and diazepam resulted in precipitation. Precedex, which is incompatible, with amphotericin B and diazepam, should not be administered simultaneously with those drugs.