This 12-month observation studied the clinical epidemiology of the "curbside" consultation process in a three-physician, private (fee-for-ser-vice), endocrinology practice that also provides consultative services to a staff-model HMO on a discounted fee-for-service basis. During the study, there were 559 curbside consultations (23.8% of which resulted in patient referrals) and 2001 formal consultations. The areas addressed most frequently were the thyroid gland, calcium, diabetes mellitus, the adrenal glands, the gonads, and the pituitary gland. Of the 513 curbside consultations by the three endocrinologists, 63.4% were from primary care providers, 8.3% from other endocrinologists, and 15.3% from other subspecialists. Physicians in the HMO accounted for a larger proportion of curbside consultations than of formal patient referrals (22.2% vs. 12.9%; p < 0.00001). The proportion of curb-side consultations resulting in formal referrals (31.6%) was higher for physicians in the HMO than for physicians in fee-for-service practice, although this difference was not statistically significant (p = 0.04). The data suggest that curbside consultations constitute an appreciable workload, that a minority of such consultations result in patient referrals, and that curbside consultation is used to a greater extent in the managed care setting. Questions about the impact of this on resource use and outcomes await further study. (C) Lippincott-Raven Publishers.