The purpose of this study was to evaluate the effect of acute caffeine ingestion on the maximal accumulated oxygen deficit (MAOD) and short-term running performance. Nine well-trained males performed a preliminary assessment and. at least 4 days later, a supramaximal run to exhaustion. Their VO₂max values were determined, and the MAOD test at an exercise intensity equivalent to 125% VO₂max was performed. Caffeine (5 mg ⋅ kg⁻¹) or placebo was administered 1 hr prior to the MAOD in a double-blind, randomized cross-over study. In comparison to the placebo condition, subjects in the caffeine condition developed a significantly greater MAOD and increased their run lime to exhaustion. However, posl-MAOD blood lactate concentration ([HLa]) was not different between trials for caffeine and placebo. Caffeine ingestion can be an effective ergogenic aid for short-term, supramaximal running performance and can increase MAOD. However, these results do not appear to be related to an increased [HLa).