Samiria river.-Field work was carried out along the Samiria river, in the Pacaya-Samiria National Reserve, northeastern Peru (Loreto), at the end of the rainy season, May-June 1990. More than a thousand morphospecies belonging to at least 39 families of spiders were collected from various canopy and understory microhabitats by using a combination of fogging and conventional sampling techniques. Over half of the species belong to only three families: Salticidae (19%), Theridiidae (16%), and Araneidae (18%). Diversity and abundance for the former two families were higher in the canopy, while for the last one they were higher in the understory. The highest number of species (151) was found in one of the most heterogeneous canopy microhabitats. A few species accounted for 1-3% of the adult spiders, the great majority did not reach 0.5% of the total number of adults collected (5,895 indiv.). The two most complex categories of microhabitats from the canopy and the understory strata appeared to be moderately distinct, 59% of species were present in only one or the other. However, single sets of microhabitats from both strata exhibited a narrow spider species overlap, on average, 89% of complementarity.