The aim of this study was to examine selected substrate and hormone responses to 30-min treadmill runs performed several days before and after a competitive marathon (42.2 km) to determine the time course for return of altered responses to pre-race levels. Six experienced male runners (30.8 +/- 9.1 years) ran at their predicted race pace (77.1% +/- 4.1% of VO2max) 8-7 days prior (S-1) to the Boston Marathon and 2-3 (S-2), 6-7 (S-3), and 13-14 days (S-4) post-marathon. All 30-min runs were performed in the morning at a constant time for each subject following a 12-h fast. Blood samples were drawn immediately before and immediately after (within 1 min) the 30-min runs. Post-exercise glucose responses were higher (P less than 0.05) during S-2 and S-3 compared with S-1 values. S-2 post-exercise lactate concentrations were also higher than the corresponding S-1 value. Pre-exercise free fatty acid (FFA) levels during S-4, and the post-exercise FFA values during S-2, S-3, and S-4, were lower (P less than 0.05) than the corresponding S-1 concentrations. Pre- and post-exercise alanine levels during S-2 were higher (P less than 0.05) than the S-1 values. Both pre- and post-exercise insulin levels during S-2, S-3, and S-4 were greater (P less than 0.05) than corresponding S-1 concentrations. Glucagon concentrations were unchanged across all sessions.(ABSTRACT TRUNCATED AT 250 WORDS)