Purified diets containing 5 graded levels of lysine were fed to young and growing pigs to determine the lysine requirement for growth and maintenance. A model was developed to subdivide the lysine requirement for the maintenance from requirement for growth. From this model, the lysine requirement for growth was 18.018 and 19.431 g/kg live weight gain and the maintenance requirement was 0.115 and 0.033 g per unit of metabolic body size at each stage of growth, respectively. In the young pigs, the lysine requirement for growth was 0.950 g/g N gain and the maintenance for growth was 0.114 g per unit of metabolic body size. The breakpoint of plasma lysine concentrations was 8.695 and 13.464 g/d, respectively. Expected requirements obtained from these formulae were in general agreement with previous estimates. Based on weight gain vs N gain equation, about 7.92% of the retained protein was comprised of lysine as compared to 7.11%, the mean lysine content of pig muscle CP.