PURPOSE: The purpose of this study was to determine whether adiposity affects the attainment of (.)VO2max. METHODS: Sixty-seven male and 68 female overweight (body mass index (BMI) = 25-29.9 kg.m) and obese (BMI > or = 30 kg x m) participants undertook a graded treadmill test to volitional exhaustion (phase 1) followed by a verification test (phase 2) to determine the proportion who could achieve a plateau in (.)VO2 and other "maximal" markers (RER, lactate, HR, RPE). RESULTS: At the end of phase 1, 46% of the participants reached a plateau in (.)VO2, 83% increased HR to within 11 beats of age-predicted maximum, 89% reached an RER of > or = 1.15, 70% reached a blood lactate concentration of > or = 8 mmol x L, and 74% reached an RPE of > or = 18. No significant differences between genders and between BMI groups were found with the exception of blood lactate concentration (males = 84% vs females = 56%, P < 0.05). Neither gender nor fatness predicted the number of other markers attained, and attainment of other markers did not differentiate whether a (.)VO2 plateau was achieved. The verification test (phase 2) revealed that an additional 52 individuals (39%) who did not exhibit a plateau in (.)VO2 in phase 1 had no further increase in (.)VO2 in phase 2 despite an increase in workload. CONCLUSIONS: These findings indicate that the absence of a plateau in (.)VO2 alone is not indicative of a failure to reach a true maximal (.)VO2 and that individuals with excessive body fat are no less likely than "normal-weight" individuals to exhibit a plateau in (.)VO2 provided that the protocol is appropriate and encouragement to exercise to maximal exertion is provided.