Ninety five pairs of lungs obtained from individuals (Filipinos) with ages ranging from 17 to 85 years, of both sexes, were dissected to demonstrate the patterns of bronchial branching. The lobar bronchi were followed as far as their tertiary subdivisions. The segmental bronchi were identified on the basis of the surface area ventilated or supplied, and were named following the terminology introduced by Jackson and Huber The average frequencies of the different modes of division of the lobar bronchi giving rise to the segmental bronchi were obtained by combining the results reported in the studies of Dualan and the data gathered in this study RIGHT LUNG: The right upper lobe bronchus divided by trifurcation in 20 of the cases: and, by bifurcation in 26 of the cases. The middle lobe bronchus divided by bifurcation into the lateral-medial pattern in 81.5 of the cases; and, the lateral or medial segmental bronchus was given off from either the upper or lower stem bronchus in 10.5 of the cases. The lower lobe bronchus gave as its first branch, the superior basal segmental bronchus, in 78 of the cases; and, it is given off from the middle lobe bronchus in 12 of the cases. The medial basal segmental bronchus is given off at the same level but separately with 2 or 3 other basal bronchi in 44 of the cases; and, it is given off from a bifurcation of a common trunk with one of the basal bronchi in 31 of the cases. The anterior basal segmental bronchus is given off at the same level but separately with 2 or 3 other basal bronchi in 46.5 of the cases; and, it arises from a bifurcation with one of the basal bronchi in 38 of the cases. The lateral basal segmental bronchus is given off at the same level but separately with 2 or 3 other basal bronchi in 47.5 of the cases; and, it arises from a bifurcation of a common trunk with one of the basal bronchi in 40 of the cases. The posterior basal segmental bronchus arises in conjunction with the lateral basal bronchus from a bifurcation of a common trunk in 59 of the cases; and, it is given off at the same level but separately with 2 or three other basal bronchi in 16 of the cases LEFT LUNG: The Upper Lobe Bronchus - Upper Division: - This bronchus divides by bifurcation in 56 of the cases; divides by trifurcation in 34 of the cases; and, occured as the "Split" type in 7.5 of the cases. Lower Division; this bronchus divides by bifurcation into the superior and inferior branch in 82 of the cases; and, divides by trifurcation in 8 of the cases. The Lower Lobe Bronchus: - this bronchus gave as its first branch, the superior basal segmental bronchus, in 75 of the cases; and, originated from any of the basal bronchi in 2 of the cases. The subsuperior segmental bronchus (including the accessory subsuperior bronchus) is given off as a single trunk from the basal stem bronchus in 19 of the cases; and, the occurrence of an accessory subsuperior bronchus in 12 of the cases. The basal stem bronchus, divides by trifurcation in 25 of the cases; and, by bifurcation in 28 of the cases. It undergoes an irregular pattern of branching in 56 of the cases. The antero-medial basal segmental bronchus is given off from a common trunk arising from the basal trunk in 54 of the cases; and, the anterior and medial basal segmental bronchi are given off separately in 6 of the cases. The lateral basal segmental bronchus is given off from a common trunk with the posterior basal segmental bronchus in 41 of the cases; and, arises from a trifurcation with two other basal bronchi separately in 34 of the cases. The posterior basal segmental bronchus is given off from a common trunk with the lateral basal segmental bronchus in 42 of the cases; and, it arises from a trifurcation with two other basal bronchi in 38 of the cases. (Summary)