Pre-harvest production of maize in Kenya was estimated using radiometry and aerial photography. Twenty-five strata covering 61 000 km2contained 900 000 ha of maize. The ratio of near-infrared (NIR) to red reflected from maize fields was measured with airborne radiometers over 100 fields. The actual yields were measured immediately prior to harvesting. A regression (R2= 0·77) predicting yield from NIR/red was obtained. A systematic radiometric survey was conducted and the regression was used to estimate the pre-harvest yield in all maize growing strata. The average nation-wide yield was 372 t/km2, giving a total production of 3360 kt.