Although neurospyhilis has become a rare disease, requests for cerebrospinal fluid (CSF) syphilis serology tests at the Colorado Department of Health have increased in recent years. Because of the low rate of positive results, questionnaires were sent to the physicians who requested these tests to determine the criteria for their use. Neurosyphilis was neither suspected nor an important consideration to rule out in 63 percent of the 337 patients sampled. Of the patients whose ages were specified, more than half were under age 40. No concomitant reports of blood serology were available for 63 percent of the study patients, and only 13 percent of the available blood serology reports indicated reactivity. One of the two patients with positive test results was appropriately treated, but the other patient for whom the test was ordered 'routinely' to rule out neurosyphilis was lost to followup. One-half of the tests were requested by neurologists, neurosurgeons, and orthopedists. The survey findings indicated that most of the CSF serologic tests for syphilis were done without appropriate preliminary testing for patients who had no evidence of syphilis by physicians who perform lumbar punctures as a consequence of their specialties. The authors recommend that use of the test be reviewed in light of the changing epidemiology of the disease. They further suggest that directors of laboratories performing CSF serologic tests are in a unique position to initiate an educational exchange and a consequent change in physicians' behavior.