The feeding deterrent activity of sapwood extracts of sugar pine,Pinus lambertiana Dougl., and related compounds was determined against immatures of the western drywood termite,Incisitermes minor (Hagen). A bioassay was designed to quantify reductions in termite feeding caused by deterrent chemicals. Crude extracts and isolated fractions of sugar pine were deterrent and not preferred byI. minor at 0.5 mg/cm(2). Fatty acids occurring in sugar pine extracts had a broad range of deterrent activity. Long-chain saturated fatty acids were deterrent at 0.25 and 0.05 mg/cm(2). Unsaturated or intermediate length (C8-C14) acids, many not found in sugar pine wood, were less active than long-chain saturated acids. Related alpha-halogenated compounds were highly deterrent at 0.05 mg/cm(2) regardless of chain length or presence of a carboxylic acid moiety. Deposits of 2-iodooctadecanoic acid reduced termite feeding at 5 μg/cm(2), while 2-bromooctadecanoic acid had deterrent activity comparable to commercial wood preservatives. None of the halogenated compounds tested were termiticidal.