Forced expiratory flows at functional residual capacity (VmaxFRC) by the rapid compression technique and functional residual capacity (FRC) by the helium dilution technique were assessed in 112 normal infants with a mean age of 10.7 months (range, 1.0-31.0). In predicting FRC, log transformation was appropriate and body length was the best predicator. For VmaxFRC, age was a better predictor than length, and logarithmic transformation was not required. In(FRC) = -5.465 + 2.49 x In(length) SD = 0.178; r2 = 0.83 VmaxFRC = -397 + 9.36 x (age) SD = 88; r2 = 0.52 There were no gender differences for FRC or VmaxFRC; however, male infants exposed to passive cigarette smoke tended to have lower flows than male infants not exposed (P < 0.07). This study establishes normative values for VmaxFRC and FRC in infants between 1 and 31 months of age, and suggests that passive cigarette smoke exposure has an adverse effect upon forced expiratory flows in male infants.