VAN DUSER, B. L. and P. B. RAVEN. The effects of oral smokeless tobacco on the cardiorespiratory response to exercise. Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 389–395, 1992. The purpose of this investigation was to determine the effects of oral smokeless tobacco (OST) usage on oxygen uptake (V̇O2), cardiac output (𝑄̇c), stroke volume (SV), heart rate (HR), and plasma lactate concentration (Lc) during rest and exercise. Fifteen asymptomatic subjects were recruited from 18 to 33-yr-old male users of OST. Comparisons of the responses of V̇O2, 𝑄̇c, SV, HR, and Lc were made between 2.5-g OST and placebo experimental conditions during rest and at 60% and 85% maximal V̇O2 treadmill exercise. Plasma nicotine concentrations (Nc) were determined by radioimmunoassay. There were significant increases in HR and Lc and a decrease in SV during rest and at 60% and 85% maximal exercise (P < 0.05). Furthermore, there were no significant differences in maximal HR, Lc, and V̇O2 (P > 0.05). In conclusion, these data indicate that the increased Nc incurred by OST usage increases anaerobic energy production and produces an increased tachycardiac response to a given relative submaximal workload.