Eleven obese women progressively increased periods of walking each day for one year or longer while no dietary restriction was imposed. No weight loss occurred until walking exceeded 30 minutes daily. Generally, weight loss paralleled length of time spent walking. When a certain amount of walking was maintained and weight stabilized at a lower level, more weight loss occurred when walking was increased. Weight loss was slow and proceeded at a rate much less than anticipated if no compensatory increase in food intake had occurred. A marked decrease in skinfold thickness over the upper part of the arm occurred, suggesting that loss of fat accounted for most, if not all, of the weight loss.