The measurement of maximal inspiratory and expiratory pressures at the mouth (MIP and MEP, respectively) provides a noninvasive clinical method for evaluating the strength of respiratory muscles. In an attempt to reconcile the widely divergent normal values reported in the literature for healthy adolescents, we have measured, using simple manometry, MIP and MEP in 112 white subjects, 76 adolescents and 36 healthy adults. For female adolescents the values for MIP and MEP were 76 +/- 25 and 86 +/- 22 cm H2O, respectively, and were significantly less than those for male adolescents (p less than 0.01), whose mean values were 107 +/- 26 and 114 +/- 35 cm H2O, respectively. Mean values for adolescents were comparable to values measured in adult control subjects, and for both adolescents and adults, mean values approximated the lower end of the previously reported ranges of normal values in healthy subjects. Thus, MIP and MEP in healthy adolescents are significantly greater in male subjects than female subjects, but are comparable to those of healthy adults of the same sex. Furthermore, these studies suggest that the choice of normal values for MIP and MEP must take into account significant methodologic differences among laboratories.