Athletes are susceptible to upper respiratory tract infection (URTI) during intense training and after major competition; high rates of URTI have also been associated with the overtraining syndrome (staleness). Secretory immunoglobulin A (IgA), the predominant immunoglobulin in mucosal secretion, is a major effector of resistance against pathogenic microorganisms causing URTI. Previous work has shown that salivary IgA levels decrease after a single bout of intense prolonged exercise. The purpose of these studies was to examine the IgA response to various exercise conditions. Whole, unstimulated saliva was obtained before and after exercise. IgA concentration (microgram.mg protein-1) was measured by ELISA and IgA secretion rate (microgram.min-1) calculated. Study 1: Recreational joggers ran on a treadmill for 40 min at 55% and 75% VO2peak and competitive distance runners ran for 90 min at the same intensites. In both groups, IgA secretion rate did not change significantly after exercise at either intensity. Study 2: Competitive runners ran on a treadmill for 90 min at 75% VO2peak on 3 consecutive days. IgA secretion rate decreased 20 to 50% after exercise (p < .001). Post-exercise IgA secretion rates were significantly lower (p < .05) on days 2 and 3 compared with day 1. Study 3: Elite swimmers were followed over a 6 month season, with IgA concentration measured at 5 times. Throughout the season, IgA concentration was significantly (p < .05) lower in stale compared with well-trained swimmers.(ABSTRACT TRUNCATED AT 250 WORDS)