FALK, B., O. BAR-OR, R. CALVERT, and J. D. MACDOUGALL. Sweat gland response to exercise in the heat among pre-, mid-, and late-pubertal boys.Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 313–319, 1992. Sweating rate (SR) of boys is lower than that of men. To assess the association between the response of individual sweat glands and physical growth and maturation, three groups of circumpubertal boys cycled at 50% &OV0312;O2maxin a climatic chamber (42°C, 20% relative humidity). Based on Tanner staging (pubic hair), 16 were classified as prepubertal (PP, Tanner 1), 15 as midpubertal (MP, Tanner 2–4), and five as late-pubertal (LP, Tanner 5). Population density (PD) of the heat-activated sweat glands, the mean area of sweat drops (DA), and the proportion of skin covered by sweat (%A) were measured by skin photography and computer-assisted imaging analysis. Other measurements included rectal and skin temperatures (Tre, Tsk, respectively), heart rate (HR), and total body SR. The rise in HR, Treand Tskdid not differ among groups. Whole body SR was significantly higher in the LP group compared with PP (PP = 4.95 ± 0.23, MP = 5.79 ± 0.20, LP = 6.70 ± 0.42 ml · min-1· m-2) (mean ± SEM). PD was significantly higher in the PP group (PP = 128 ± 8, MP = 97 ± 9, LP = 74 ± 9 glands · cm-2), while DA was higher in the LP group (PP = 5.47 ± 0.59, MP = 6.92 ± 0.47, LP = 12.83 ± 1.41 ·m2· 104). A did not differ among groups. The calculated SR per gland was higher among the LP groups compared with the less mature ones (PP = 4.6 ± 0.3, MP = 7.2 ± 0.8, LP = 9.6 ± 1.0 nl · min-1). SR per gland was inversely related to PD (r= −0.88), and positively related to DA (r =0.67), but was not related to %A (r= −0.08). We conclude that physical growth and maturation are accompanied by decreased density of heat-activated sweat glands, but an increased sweat drop area. This is reflected by an increased SR per gland.