We propose an analysis of the branching pattern of the conducting airways of the human bronchial tree, based on classifying airways by diameter rather than by some essentially topological measure of their position in the whole lung. A diameter-based statistical reconstruction technique is applied to the partial measurements of airway dimensions made by Raabe et al. (1976), to quantify some aspects of bronchial geometry likely to influence transport processes in the lung. We give predictions for the total number of airways with each diameter, and for the partitioning of the total bronchial wall area and airway volume between airways of different diameters. We also consider the variability of the lengths of different pathways through the bronchial tree, and using a simple model for the distribution of air flow in the lung, we predict how the average flow velocity depends on airway diameter. Comparison of these results with equivalent predictions derived from Weibel's symmetrical lung model shows qualitative differences, which probably result from Weibel's use of extrapolation techniques to compensate for the lack of data on smaller conducting airways. Comparison with the predictions of Horsfield and Cumming's asymmetrical lung model shows generally good agreement, although there are significant differences relating to the asymmetry of bifurcations and to the diameter-dependence of the flow velocity in the smallest conducting airways.