The present study evaluated the utility of a portable metabolic measurement system, the Aerosport TEEM 100. A total of 505 data points [242 from incremental (INC) and 263 from constant load (CL) exercise] were collected on 12 subjects (age = 25 +/- 4 yr), by placing the Aerosport TEEM 100 medium flow pneumotach and mouthpiece in-line with a validated system, the Rayfield system. When VO2 values were separated into categories (< 1.5, 1.5-2.0, 2.0-2.5, 2.5-3.0, > 3.0 l.min-1), there was a small but statistically significant difference between the two metabolic measurement systems for VO2, VCO2, VE, RER, %ECO2, and %EO2 during both INC and CL exercise and measurement error for VO2 ranged between 2% and 11%. Correlations for VO2 values during INC and CL exercise between the two systems were r = 0.95 (SEest +/- 0.18 l.min-1) and r = 0.96 (SEest +/- 0.29 l.min-1), respectively. Correlations for RER were r = 0.82 (SEest +/- 0.08) and r = 0.47 (SEest +/- 0.11), for INC and CL, respectively. Results from the present investigation indicate that the Aerosport TEEM 100 has utility for the assessment of VO2, but the estimation of carbohydrate and fat utilization from RER should be used with caution.