Fetal rhesus monkeys were treated with recombinant human epidermal growth factor (EGF) to determine if EGF can induce maturation of the tracheobronchial secretory apparatus. At 75% of gestation, EGF was administered simultaneously into both the amniotic fluid and fetal abdominal cavity at an average dose of 66 micrograms/kg body weight, by each route over a 7-d period. At the end of the treatment period, the fetuses were delivered and either euthanized immediately or after maintenance on ventilatory support for 6 h. The lungs were removed, and the trachea and one lobe of the right lung was fixed and embedded for light microscopy. The left lung was lavaged with saline, and the collected fluid was used to quantify released secretory product. Secretory product was also measured in amniotic fluid as well as in situ on histologic sections of tracheal epithelium. When the tracheas of EGF-treated monkeys were examined, the epithelium was found to be taller and to contain a greater proportion of secretory cells and a smaller proportion of intermediate cells than the control group. However, there was no significant change in the total number of cells per millimeter of basal lamina or in the proportion of the epithelial population made up of basal or ciliated cells. There was more secretory product stored in the epithelium and submucosal glands and increased quantities of respiratory secretions in both lung lavage and amniotic fluid of EGF-treated monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)