The fumigation of insecticides initiated by Gorgas and Oswaldo Cruz had its importance reduced after the introduction of DDT but is use is being resumed with the development of low toxity organophosphate insecticides. At this time, however, the technological development is different. The airplane and the helicopter allowed the spraying of insecticides under the technical grade form and, after that, machines that could be transported in vehicles to perform this task were developed. Soon after, the problem of the size of the droplets was resolved and these must be smaller than 20µ for mosquitoes. These applications at ultra low volume were initially used in Brazil against Culex quinquefasciatus and its use increased after the reintroduction of Aedes aegypti. A series of experimental trials with the aim to produce a rapid decrease in the density of this insect was initiated in 1984 by Sucam using technical grade Sumithion (Fenitrothion). Subsequently it was tried the concentration of 60% in soybean oil and then Sumithion and Malathion at 40% with good results. With the machine transported in vehicle (Leco) the flow rate was 126 ml/min with the vehicle at a speed of 10 km/hour which, in theory, corresponds to a dose of 300 ml/ha. At the slums of the city of Rio de Janeiro these, concentrations yielded very good results when applied with the aid of portable machines (Microgen and Hatsuta) using doses of 12-20 ml/house in steep areas and 4,5 ml/housein plane areas. With these machines the application of these insecticides in concentration of 25%, also in slums, yelded good results. With the portable machines it is necessary to make modifications to decrease the flow rate of the insecticide to improve the spectrum of sizes of the droplets. Based in the available literature new experiments with lower concentration are suggested.