This paper presents the results of weekly outdoor captures of adult mosquitoes on human bait, carried out in a coastal lowland farm, Granjas Calábria, in Jacarepaguá, city of Rio de Janeiro, Brazil from Augus 1981 to July 1982 in order to study their seasonal density and their frequency as to the lunar cycle. Of the 32 species obtained, Aedes scapularis, Culex crybda, Culex declarator, Culex nigripalpus, Culex saltanensis, Mansonia titillans, Phoniomyia davisi, Phoniomyia deanei and Phonlomyia theobaldi were present in every month of the year. We have placed the species in three groups according to the seasonal variation: (i) species whose desnsity was directly proportional to rainfall and temperature, developing in temporary and semi-permanent breeding-places, such as Aedes scapularis, Aedes taeniorhynchus and Culex nigripalpus; (ii) species whose frequency was independent from these meterorological factors, developing in permanent breeding-places, such as Culex amazonensis, Culex declarator and Coquillettidia venezuelensis; (iii) species whose density was inversely proportional to rainfall and temperature, also developng in permanent water, such as Mansonia titillans and Wyeomyia leucostigma. The catches performed during the last quarter moon were the most productive, although the present results are not conclusive as to indicate a clear control of the lunar cycle on moquito density.