Failure to fully recovery between training sessions has been suggested to evoke chronic fatigue, underperformance and greater immunodepression (Gleeson, 1998). It has been suggested that the alterations in neutrophil function and trafficking do not recover within 3 h (Li & Gleeson, 2004), but appear to be fully recovered within 18 h after prolonged exercise (Li & Gleeson, 2005). The aim of the present study was to determine the time course of recovery of neutrophil responses following 2 h cycling at 55% peak power. Ten healthy men (age 21.6 ± 0.9 years, height 1.77 ± 0.01 m, body mass 66.9 ± 1.8 kg, VO2max 54.2 ± 2.0 ml kg^-1 min^-1; means ± SEM) performed 2 h cycling (started at 09:00) at 55% peak power (143 ± 4 W) or a separate resting control trial in a counterbalanced order after an overnight fast, separated by at least 6 days. No food was consumed, though water ingestion was allowed ad libitum, until the trials finished at 20:00. Venous blood samples were collected at pre-exercise (pre-EX), immediately post-exercise, and at 3, 6 and 9 h post-exercise. Haematological analysis was performed using an automated cell counter. Plasma hormone concentrations were determined using ELISA kits. fMLP (N-formyl-MET-LEU-PHE)-induced oxidative burst activity was measured using a chemiluminescence (CL) assay (Knight Scientific Limited, Plymouth) and bacteria-stimulated neutrophil degranulation (elastase release) was determined as described by Li & Gleeson (2005). Results were analysed using a two-factor (trial × time) repeated measures ANOVA with post hoc Tukey tests and paired t tests applied where appropriate. The 2-h cycling bout significantly altered circulating neutrophil count (P<0.01) and functions (both P<0.01) and plasma stress hormone concentrations (P<0.01) as shown in Table 1. The impact of the cycling on neutrophil oxidative burst and degranulation capacities on a per cell basis and plasma adrenaline and cortisol, compared with resting control, recovered within 6 h, 9 h, 3 h, and 9 h post-exercise, respectively; whereas neutrophil count did not recover within 9 h post-exercise. These findings suggest that the recovery interval between exercise sessions should be at least 9 h to allow recovery of neutrophil functions in the fasted state after a bout of prolonged strenuous exercise.