The stability of thiotepa (lyophilized) 0.5 and 5 mg/mL in 5% dextrose injection was studied. Vials of lyophilized thiotepa were reconstituted with sterile water for injection to yield a solution with a nominal 10-mg/mL drug concentration. The reconstituted solution was filtered and diluted in 5% dextrose injection in polyvinyl chloride and polyolefin bags to nominal thiotepa concentrations of 0.5 and 5 mg/mL. Triplicate test admixtures were prepared and stored at 4 or 23 degrees C in normal fluorescent light. Initially and after four and eight hours and 1, 3, 7, and 14 days, samples were removed for visual evaluation, turbidimetry, and stability-indicating high-performance liquid chromatography. No incompatibilities were observed. Admixtures containing thiotepa 0.5 mg/mL retained at least 90% of the initial drug concentration for eight hours at either temperature in either type of container; after 24 hours, losses ranged from 10% to 17%. Thiotepa in the 5-mg/mL admixtures was stable for 3 days at 23 degrees C and 14 days at 4 degrees C in both container types. Thiotepa (lyophilized) 0.5 mg/mL in 5% dextrose injection was stable for eight hours at 4 or 23 degrees C. Thiotepa (lyophilized) 5 mg/mL in 5% dextrose injection was stable for 3 days at 23 degrees C and 14 days at 4 degrees C.