An experiment was carried out in 1967 to assess the effects and economics of aerial applications of pyrethrum as an aerosol spray against a high density tsetse population consisting mainly of Glossina pallidipes Aust. in northern Tanzania. Complete eradication was attempted, and six applications of a 0·4% w/v solution of natural pyrethrins, synergised with 2% piperony1 butoxide in power kerosene, were applied at three-week intervals over three square miles. Application was from a Cessna 182E fitted with one Micronair rotary atomiser. Populations of G. pallidipes, assessed from fly-path catches, were reduced 95% after three applications. The final three applications had little effect and it was considered that unfavourable meteorological conditions and full leaf cover were the main factors responsible. It is suggested that, in view of the high initial kill of the fly and the possibility of using pyrethrum economically against tsetse for human settlement schemes, further work should be carried out with this insecticide.