Patients are randomized to 1 of 2 groups to receive treatment on 2 separate occasions at least 72 hours apart. Group 1 receives the reference formulation of ddI. Group 2 receives the test formulation of ddI. Clinical evaluations, including clinical laboratory tests, are performed periodically during the study and at discharge. Serial blood samples are collected at specific time points over the 12 hours following dosing, and are used for the pharmacokinetic variables CMAX and AUC(INF). Factors used in analysis are sequence, subject within sequence, period, and formulation. Safety is assessed by monitoring adverse effects, vital signs, ECG recordings, and clinical laboratory tests throughout the study.