This report is the second of a series describing experiments with the overall aim of determining the requirements of the young pig for calcium and phosphorus (see Blair,The primary aim of this second study was to provide radiological information on the pattern of development of the limb bones of pigs up to 8 weeks of age. It was hoped that this information could be used later in assessing the adequacy of the Ca and P content of a synthetic diet.The weaning of pigs from the sow at an early age normally results in a check in liveweight gain (Smith & Lucas, 1956-7) which is probably reflected in a check in the growth of the skeleton, and therefore a suckled litter was chosen for this study. Samples of the sow's milk were withdrawn regularly for analysis to determine whether, by comparison with previously obtained data on the composition of milk from the Wessex Saddleback breed (Lodge, 1 9 5 9 the nutrition of the piglets could be regarded as normal. In addition chemical analyses were made on the whole skeletons of the pigs at 8 weeks together with radiographic density measurements of selected bones. 1963). E X P E R I M E N T A LAnimals. A Wessex Saddleback sow, known to produce good litters, was mated to a Landrace boar. She was put into a farrowing pen a few days before full term and eight piglets were born. They were weighed soon after birth and given identification marks. One weak piglet died on the 8th day.T o prevent iron-deficiency anaemia the piglets were dosed orally with a mixture of glucose and reduced iron at 3 days and at weekly intervals thereafter until supplementary food was given. At 10 days the males were castrated. Live weights were recorded weekly.At 8 weeks of age the piglets were killed by captive-bolt pistol. Radiographs. Radiographs were taken of the limbs at birth and immediately after each weekly weighing up to 8 weeks of age. The operative voltage was progressively raised from 62 kV at birth to 70 kV at 8 weeks, otherwise the radiographic ratings were kept constant at 100 mA, exposure 0 . 1 2 sec and tube focus-film distance 36 in. From the radiographs the following measurements were made with a Vernier microscope :(a) medial length of the diaphysis (shaft) only of the radius and tibia;