The fall in end-tidal and arterial P(CO2) may be delayed relative to the lactate threshold (LT) or absent, depending on the slope of the ramp exercise function. Ventilation (VE), gas exchange (V(O2), V(CO2)) and acid-base status were examined during slow (SR, 8 W x min(-1)) and fast (FR, 65 W x min(-1)) ramp cycle exercise in seven males. VE, V(O2), V(CO2), and end-tidal gas tensions (PETO2, PET(CO2)) were determined breath-by-breath. Peak V(O2) (V(O2,peak)) was similar in SR and FR. V(CO2) and VE were similar during submaximal exercise. At V(O2,peak), VE was similar but V(CO2) was lower in SR than FR. With exercise, PET(CO2) increased at work rates below LT. At WRs > or =90%-V(O2,peak), PET(CO2) decreased below 0 W values in SR but not FR. Alveolar P(CO2)2 slope (PA(CO2)) increased with increasing WRs. Above LT, PA(CO2) was lower in SR than FR. Time of expiration (TE) decreased with increasing WRs, but no difference between SR and FR was observed. The higher PET(CO2) in FR at higher WRs was attributed in part, to a higher PA(CO2) as no differences were observed in TE.