Bluegill were exposed to methoxychlor at various concentrations for 13 weeks in late summer. Fish losses were small and not attributable to methoxychlor exposure. There was no significant differences in fish growth in the three pairs of ponds. Pathologic changes occurred in tissues and organs, primarily in livers and circulatory systems. Precipitated materials were observed in major blood vessels of gills and hearts 24 hours after treatment. This material coalesced, became multivacuolated, was conspicuous in most large blood vessels of every organ during the first week after treatment, persisted through day 28, and disappeared by day 56.