The report discusses services provided by EPA's Control Technology Center (CTC) during FY90. The CTC, developed by EPA's Office of Research and Development (ORD) and Office of Air Planning Quality and Standards (OAQPS), is an innovative technical assistance program for state and local air pollution agencies and EPA's regional offices. Since the CTC's inception, its program has expanded to address more than just air toxics issues. It now addresses emission source and control technology problems associated with air toxics, particulate matter, oxides of sulfur and nitrogen, carbon monoxide, lead, PM10, and volatile organic compounds. The CTC is designed to be flexible so that it can respond quickly to many client needs as they arise. The CTC provides three categories of services: telephone HOTLINE assistance (919/541-0800), direct engineering assistance, and technical guidance. The HOTLINE permits easy access for state and local agencies to EPA personnel who can provide prompt assistance in a variety of ways, including consultations, references to pertinent literature, and access to EPA technical data and analyses. Direct engineering assistance is short-term, averaging about 3 months and providing technical assistance without regard to national utility. Technical guidance is longer term, up to a year, broader in scope, and with national applications.