In early 1976 the U.S. Environmental Protection Agency revised the National Pollutant Discharge Elimination System (NPDES) program on animal feeding operations. This study analyzes the economic impact of proposed amendments to Pollution Control Board (PCB) regulations which will accommodate Illinois law and conditions with the federal guidelines. Illinois statutes require an economic impact study for all amendments to PCB regulations. The first four proposed amendments deal with the addition of six new definitions, and making the regulations consistent with these additions. The economic impact of these new definitions is minimal and is basically a matter of terminology rather than substance. The fourth proposed amendment does expand the application of the general provisions of the Environmental Protection Act to animal feeding operations beyond just water and air pollution. Proposed amendment five may be the most critical. It specifies a new classification of large-scale animal feeding operations (between 300 and 1,000 animal units). If it is assumed that all of these operations are currently covered in case-by-case regulations, the economic impact is minimal. If, however, it is assumed that these operations, either in total or in part, would have been 'skipped' by the case-by-case designation, then the livestock industry in Illinois would bear a substantial cost.