A longitudinal study of the growth progress of monozygotic [male] triplets is reported. Measures of height, wt., various skeletal dimensions, and such phases of maturation as sexual development, eruption of permanent teeth, grip strength, etc., were made semi-an-nually. The relation of the differential growth of fat, muscle, and of bone in the arm and leg was examined. Resemblances and differences in continuing growth patterns are described and discussed. A similar pattern of development is revealed. No one pair seems to show consistently a more intimate relationship. 8 figures, each depicting several measurements, are included.