Zootermopsis is an interesting model for study of termites, especially for chemical communication. Sex specific male and female sex pheromones were shown by Pasteels (1972) in Z. nevadensis and the first trail-following pheromone of termites was discovered in the same species by Lüscher and Müller (1960) and Stuart (1961), then identified as hexanoic acid according to Hummel and Karlson (1968). The aim of our study was to identify the sex pheromones of Z. nevadensis and Z. angusticollis living in sympatry in western USA and to reinvestigate their trail pheromones after using solid phase microextraction (SPME). The components specifically present at the surface of the sternal gland producing sex and/or trail pheromones were identified by GC-MS, GC-FTIR, on line GC microhydrogenation, then synthesized and tested for their biological activity through sex attraction and trail-following bioassays. Results were statistically evaluated with t and X2 tests. The female sex pheromone (5-10 ng/individual) was identified in both species as (E)-2,6,10-trimethylundeca-5,9-dienal. In male alates, a compound specific to sternal gland (2-5 ng/individual) was identified as 4,6-dimethyldodecanal. Although not yet tested on female alates, it very probably represents the male sex pheromone. 4,6-Dimethyldodecanal also is the major specific component of the sternal gland of pseudergates and nymphs of both sexes (0.1-0.5 ng/individual). In pseudergates, the synthetic compound elicits a high trail-following from 0.1 ng/cm of trail. This molecule can be therefore considered as the trail pheromone of both species. Its stereochemistry is under investigation. Hexanoic acid, present on the whole surface of the integument of pseudergates, especially on tergites, is not a component of the trail pheromone of Zootermopsis . Hummel V.A. and Karlson P. 1968. Z. Physiol. Chem. 349 : 725-727 Lüscher M. and Müller B. 1961. Naturwiss. 27 : 503 Pasteels J.M. 1972. Experientia 28 : 105-106 Stuart A.M. 1961. Nature 4762 : 419