Community structure of odon. larvae was investigated at El Saucillo (ES) and San Francisco (SF) streams, from August 1995 to July 1996. Species richness (S), species composition, Margalef's richness index (R), Shannon-Wiener's diversity index (FT), Hill's evenness index (E), and rareness (Rs) were used to describe and compare the communities. Annual variation of the indices was examined within and among streams. Streams were significantly different in terms of physical/chemical variables, and faunistic similarity between the communities was quite low (37%). Mean larval density was highest at ES, but the remaining parameters were highest at SF, Global richness was 31 spp. and some spp. such as Hetaerina americana, Enallagma civile, Anax junius. Erpetogomphus elaps, Dythemis nigrescens, Aeshna multicolor, A. dugesi, Erythemis plebeja and the majority of Argia spp. were only found at SF. More abundant spp. at SF were Pseudoleon superbus, Telebasis salva, Libellula saturata and Enallagma praevarum, while those more abundant at ES were Paltothemis lineatipes and Argia anceps.