Work done in this laboratory on mosquito attractants and repellents often involves the use of 8 dual-port olfactometers (Schreck, Gouck & Smith, 1967, J. Econ. Entomol. 60: 1188–90). The olfactometers are supplied with a 661 liters/sec (1400 cfm) flow of conditioned, outside air, the humidity of which has been generated by a water spray and controlled by a mechanical, hair-type humidistat. Because of the original systemʼs excessive set point drift and control band width (± 10% RH), a new humidity generation, monitoring, and control system was developed.