To measure the additional costs of office-based laboratory testing due to the implementation of the Clinical Laboratory Improvement Amendments of 1988 (CLIA '88), using cholesterol screening for children as an example. Four- to ten-year-old children who received their well child care at one of seven participating pediatric practices were screened for hypercholesterolemia. The average number of analyses per day and days per month were derived from the volume of testing completed by the practices. Nurses and technicians time in the screening process were measured and personnel costs were calculated based on salary and fringe benefit rates. Costs of supplies, analyzing control samples, instrument calibration, and instrument depreciation were included. Costs estimates of screening were then completed. CLIA '88 implementation costs were derived from appropriate proficiency testing and laboratory inspection programs. In six practices completing a low volume of testing, 2807 children (5 to 6 children per week) were screened during the observation period, while 414 (about 25 children per week) were screened in one high-volume practice implementing universal screening over a 4-month period. For the six low-volume practices, the cost of screening was $10.60 per child. This decreased to $5.47 for the high-volume practice. Estimated costs of CLIA '88 implementation, including additional proficiency testing and laboratory inspection, added $3.20 per test for the low-volume practices, and $0.71 per test for the high-volume testing. Implementation of CLIA adds significantly to the cost of office-based chemistry laboratory screening. Despite these additional expenses, the cost of testing is still within a reasonable charge for laboratory testing, and is highly sensitive to the volume of tests completed.