The report documents activities of EPA's Control Technology Center (CTC) during its fifth year of successful operation in providing technical assistance to state, local, and federal air pollution control agencies. In fiscal year 1991 (FY 91), the Center also began providing limited technical assistance to the private sector in compliance with mandates of the 1990 Clean Air Act Amendments. The report documents technical and administrative efforts during the period to respond to increased demands from the pollution control community for technical assistance. The 90% increase in HOTLINE calls resulted from an increase in calls from governmental agencies and the additional calls from the private sector. In addition, each of the other CTC services experienced significant increases. The RACT/BACT/LAER Clearinghouse experienced a 250% increase in accesses for FY 91. In its first months of operation, the CTC's Bulletin Board System averaged 79 accesses a week. Finally, more than 4,000 CTC documents were mailed during FY 91. These increases are evidence that the CTC is providing a valuable service to the air pollution control community.