Summary This paper presents an experimental study on the erosion of loose beds of sand and polystyrene by circular turbulent wall jets ol" air and water. Characteristics of the scour hole have been observed during its growth and also in the final asymptotic state. These profiles have in general been found to be similar when expressed in dimensionless forms with some dispersion near the ridge which forms at the downstream end of the hole. The length scales (made dimensionless with the jet diameter) and the dimensionless characteristic time have been found to be functions of mainly the densimetric Froude number. Some observations have also been made on the behaviour ol'the jet in the asymptotic erosion state.