This study compared the classic discontinuous Taylor et al. (1955) protocol to a continuous version of the same protocol to evaluate maximal physiological responses, and the quantitative values and incidence of achievement of the various maximal oxygen uptake (VO2max) criteria in 10 males (24.1 +/- 2.5 yr). Criteria were a plateau in VO2 (change < 2.1 ml.kg-1.min-1), HR = age adjusted maximal, PER > or = 1.15, and lactate > 8 mmol.l-1. Values for VO2max (56.8 +/- 4.7 vs 55.8 +/- 4.2 ml.kg-1.min-1), ventilation (150.7 +/- 16 vs 149.5 +/- 17.5 l.min-1 BTPS), and HR (186.3 +/- 7.7 beats.min-1 vs 191.7 +/- 6.7 beats.min-1) were similar (P < 0.05) between the discontinuous protocol (DT) and the continuous protocol (CT), respectively. Values for RER (1.28 +/- 0.05 vs 1.22 +/- 0.05) and lactate (14.3 +/- 2.7 vs 11.9 +/- 2.7 mmol.l-1) were greater (P < 0.05) on the DT than the CT. Criteria achievement were the following: 40% (CT) and 10% (DT) for HR; 50% (CT) and 60% (DT) for a VO2 plateau; and, 90% (CT) and 100% (DT) for RER and lactate. It is concluded that a VO2 plateau is not a prerequisite for defining VO2max and is of limited use as the primary objective criterion for evaluating the quality of a graded exercise test. Therefore, the achievement of secondary objective criteria, specifically RER and lactate in combination, increases the likelihood that the highest VO2 value achieved is VO2max.