Choice and non-choice bioassays were used to examine deterrence in vitro and in vivo of Tetranychus urticae Koch. In vivo deterrence of leaflets from 11 Lycopersicon hirsutum accessions as well as the tomato cultivar `Ace 55' was measured as was in vitro deterrence of their leaf hexane extracts. Leaf surface chemistry was examined by gas chromatography. All 6 accessions of L. hirsutum f. hirsutum contained sesquiterpene hydrocarbons. Each of these extracts also contained one or a few late eluting components. All were deterrent in vitro and 5 out of the 6 were deterrent in vivo. The one lacking in vivo deterrence had low density of type IV trichomes. All 5 accessions of L. hirsutum f. glabratum contained methyl ketones. These accessions were less deterrent in vitro and 4 out of the 5, less deterrent in vivo. The one accession having high in vivo deterrence also had high density of type IV trichomes. `Ace 55', having few hexane extractable compounds was neither deterrent in vitro nor in vivo. Within an accession, secretions from different types of trichomes shared similar chemical profiles and were similar to leaf profiles.