Evidence exists that estrogen metabolism has a role in the pathogenesis of recurrent respiratory papillomatosis (RRP). This disease has a papillomavirus etiology and is characterized by recurrent benign tumors with a significant propensity to become malignant. We have measured the systemic transformation of estrogen using an enzyme-linked-immunoassay to measure estrogen metabolites in the urine of patients with RRP and compared these ratios to the severity of RRP, a measure of the average growth rate of papillomas. Our results show an inverse relationship between the ratio of C-2 to C-16 alpha-hydroxylated estrogens and the severity of RRP. In a pilot study, patients consumed cruciferous vegetables to induce C-2-hydroxylation. In this group of patients, an increase in the ratio correlated with an improvement in RRP. The ratio did not change in a subset of these patients, and their RRP did not improve. Regardless, the ratio correlated with severity of their RRP.