Rock climbing is a multi-discipline activity that encompasses forms such as bouldering, top roping and lead climbing on natural and artificial climbing surfaces. A major focus of research has been explanation of physiological functioning. More recent research indicates that anxiety levels are elevated for less experienced climbers and in response to lead climbing ascents. Research regarding the demands of rock climbing has placed a lesser focus on the interaction of psychological and physiological factors. The objective of this study was to examine the effects of an on-sight lead climb on the physiological and psychological demands of the climb in comparison with a subsequent lead climb. Ten intermediate level climbers volunteered to complete the two climbing trials, on-sight lead climb (OSLC) and second lead climb (LC2). Climb time, lactate concentrations (baseline, pre climb, post climb and 15 min post climb), heart rate (1 min pre climb, peak HR, 1 min post climb and average climb across the duration of the climb), oxygen consumption, pre climb anxiety (CSAI-2R) were assessed for each climber for both trials. Results indicated that there were significant differences in self reported pre climb somatic and cognitive anxiety (t₍₉₎ = 2.79, p = 0.01, t₍₉₎ = 1.94, p = 0.043), climb time (t₍₉₎ = 3.07, p = 0.0052) and post climb lactate concentrations between the climbs (t₍₉₎ = 2.58, p = 0.015). These results indicate that psychological as well as physiological stress impact upon the response to rock climbing. The higher anxiety levels associated with an OSLC are likely to have influenced the physiological responses for the intermediate climbers in this study. Future studies should take into account the type of climbing, experience of climbers and the number of ascents as well as taking into account the interaction between physiological and psychological factors in response to rock climbing.