There is a continuing effort at identifying chemopreventive agents that might be useful in preventing cancer of the lung. In the present study, the effects of myo-inositol and dexamethasone on benzo[a]pyrene (B[a]P)-induced pulmonary adenoma formation in female A/J mice was investigated. A diet containing 3% myo-inositol fed beginning 1 week after B[a]P administration reduced the number of pulmonary adenomas by 40% but did not prevent forestomach tumors, which also occur in this experimental model. Under the same conditions, dexamethasone, 0.5 micrograms/g diet, inhibited pulmonary adenoma formation by 57% and also inhibited forestomach tumor formation to a similar extent. Feeding a diet containing both myo-inositol and dexamethasone resulted in an additive effect on the inhibition of pulmonary adenoma formation. The combination of myo-inositol plus dexamethasone produced almost identical inhibition of forestomach tumor formation to that of dexamethasone alone. The results of the present study are preliminary, but may provide a basis for future investigation into strategies for chemoprevention of pulmonary neoplasia.