The purpose of this 150 day feeding study was to determine the effects of unwanted contaminats in technical pentachlorophenol (PCP) in dairy cattle by comparing them to pure PCP and non-exposed animals. Parameters studied included clinical examination, weight gain, hoof growth, hematology and clinical chemistry, gross and histopathology, electron microscopy, immunology, hepatic enzyme induction, and chemical analysis of tissues. Preliminary data indicate that the technical compound is significantly more toxic than pure PCP.