The compatibility and stability of aminophylline-dextrose injection admixtures were investigated. Aliquots of 5% dextrose injection, 0.9% sodium chloride injection, and 5% dextrose and 0.9% sodium chloride injection were studied for these physiochemical properties: pH, color, clarity, absorbance in a spectrophotometer at 400 nm, and hydroxymethylfurfural (HMF) content. Aminophylline injection was added to the solutions, and aliquots were withdrawn after 0, 6, 24, and 48 hours of storage at 5, 25, 35, and 55 degrees C for testing of the physiochemical properties and aminophylline content. An aminophylline admixture in 5% dextrose injection was passed through an in-line filter (IVEX-2), and eluents were collected for aminophylline assay and for testing the above physiochemical properties. HMF and theophylline were assayed to high-pressure liquid chromatography (HPLC). The aminophylline concentration remained constant in all admixtures studied. A yellow color developed in dextrose-containing aminophylline admixtures stored at 25, 35, and 55 degrees C for 48, 24, and 6 hours, respectively. HMF concentration, pH, and clarity remained within compendial limits. The in-line filter did not retain active ingredients or alter the physiochemical properties of the admixture. Solutions that were yellow showed additional peaks on HPLC. HMF seemed to be a precursor for this yellow color, inasmuch as HMF concentration increased with increasing color intensity. It is concluded that aminophylline-dextrose admixtures are visually and chemically stable for 48 hours when stored under refrigeration or at room temperature.