A total of 4418 mosquitoes caught by three collection methods at two levels in the forest near Belém, Brazil, were dissected to determine the proportion of parous individuals. About two-thirds of the mosquitoes belonged to Culex (Melanoconion) portesi Senevet & Abonnenc and C. (M.) taeniopus D. & K. The dissection technique entailed dissecting out the ovaries for examination of the tracheoles, whilst preserving the rest of the mosquito for later processing for virus recovery. Analysis of the results showed that, although significant differences were found in the parous rates from samples caught off human bait, and from mouse-baited Trinidad no. 17 and blower traps, these differences were unlikely to be of practical value when compared to differences in catching ability and ease of operation of the methods. In all, 2771 mosquitoes were classed as parous, and these when inoculated into baby mice in 142 pools yielded 14 isolations. It was concluded that the technique used did not reduce the likelihood of isolating viruses from the dissected mosquitoes.