Systematic and distribution data are provided for 9 species of Culex (Melanoconion) collected in the provinces of Chaco, Corrientes and Santa Fe in northeastern Argentina during 1978-1980. Culex ocossa Dyar and Knab 1919 and plectoporpe Root 1927 are recorded for the first time from this area. Brief discussions, including preliminary arbovirus data, of ocossa and delpontei Duret 1969 are presented.