none The influence of relative humidity on adults of the Braconid ectophagous parasite Bracon hebetor Say, was investigated. Studies were made at 25 degree C, and constant relative humidities of 40%, 60% and 80%. Data were collected on egg production/female, adult longevity, pre-oviposition, oviposition and post-oviposition periods. It was found that the relative humidity considerably affected the above mentioned biological criteria. Raising relative humidity from 40% to 80 decreased the egg production, adult longevity, pre-oviposition and oviposition periods and elongated the post-oviposition period. The most favourable condition of which to liberate the parasite for pest control is probably just under 25 degree C, and 60% RH.