Brussels sprouts (Brassica oleracea var. gemmifera DC., Jade Cross) require no potassium fertilizer on Prince Edward Island soils if exchangeable soil K as determined by neutral 1 N ammonium acetate exceeds 100 ppm. Below 75 ppm exchangeable soil K, 186 kg K/ha must be applied for maximum yields. Potassium treatments increased yields at only three of 12 locations studied. Leaf tissue potassium concentration was significantly increased at all locations by the fertilizer treatments. Neutral 1 N ammonium acetate for determining exchangeable K was the best soil analysis extract among those tested for measuring available potassium. Tissue analysis gave no information beyond soil analysis for predicting potassium fertilizer requirements on any soil studied.