SUMMARYA passive optical device has been developed for the ground-based in situ measurement of liquid water content, L, in clouds. Light scattered at five, computationally selected, small forward angles is collected andwith the application of appropriate weighting factors -combined to give a response which is linearly proportional to L over the droplet diameter range I to 80pm.L can be measured to within ?0.05gm-' at a frequency of up to 100Hz. thus permitting fluctuations in the liquid water content of clouds to be examined on spatial scales of less than one metre. A miniaturized version of the device -for airborne usage -is under development.