Late season potassium deficiency symptoms are widespread and attention is being refocused on the nutritional needs of the cotton. A recent survey of the Mississippi State Soil Testing Laboratory tests found one third of the soil samples received during a recent 12 month period tested either low or medium for K. Knowledge of the relationship between tissue K content and cotton growth is limited. With emphasis on site-specific agriculture, such information is needed to diagnose reasons for low producing areas. We conducted two experiments to determine the rates of growth and other growth related processes in response to different tissue K contents. One experiment was conducted in naturally-lit plant growth chambers. Cotton cultivar, DPL NuCoTN 33, was planted in sand on 2 May, 1996. The plants were provided adequate water and nutrients needed until first square, then variable amounts of K was provided, but the plants were always well-watered and all other nutrients provided sufficiently. The plants were grown at 30/22°C day/night temperature throughout the period. Organ K, photosynthesis, dry matter accumulation, flower/boll retention, plant height, leaf area, node development and chloroplast structures were monitored. A second experiment was conducted outdoors. Leaf K, growth parameters, and boll mass and boll components were monitored.