Studies of bronchial gland enlargement in chronic bronchitis have concentrated on gland mass rather than individual glands and their reactions. Except in fetal tracheas, systematic attempts to count the number of tracheobronchial submucous glands have not previously been reported. In the study reported here the numbers of glands were counted both by observing their duct openings directly and in serial sections. Both methods had defects but the serial section method was the more reliable although the more arduous. The results are presented as duct openings/mm2 of airway wall and shown to be of the same order as the only previously reported observation (1/mm2). The serial section results for 1 smoker and 1 non-smoker revealed a range of 1.80-0.58 duct openings/mm2 in the smoker and 1.31-0.40 duct openings/mm2 in the non-smoker along the generations of the main, upper lobar, lingular, and inferior lingular bronchi. The mean volume/gland, a new measurement is also reported for each generation. Bifurcation zones were studied for the first time. In both cases the numbers and mean size of the glands were greater proximally and declined progressively along the airway generations, but in the smoker the glands were consistently more numerous and larger than in the non-smoker. Statistical analysis of 2 cases must be limited but the results provide baseline data for morphometrists and suggest, as a hypothesis for further examination, that smoking may be associated with the development of additional tracheobronchial glands.