The primary purpose of the biological studies in connection with the Ohio River Pollution Survey was twofold; first, to determine present biological conditions as a record to be compared with conditions after future changes due particularly to remedial measures which may be instituted, and second, to determine the effect, particularly of a destructive nature, of present sources of pollution on stream biological communities and fish life as a guide in judging the need for corrective measures. Secondary purposes include determination of what biological and chemical conditions may be typical of different pollutional situations, what factors under man's control are involved in creating these situations, and what combinations of these conditions may be allowed for designated stream uses. (Author)