Objectives: The objective of the present study was to find serum sodium, potassium, urea, BUN, glucose, total serum proteins, serum albumin, serum globulin and AG ratio in breastfed and non breastfed infants taking formula or fresh milk. The next objective of the present study was to determine and compare plasma osmolarity in breastfed and non breastfed group of infants by the calculated and the estimated methods. Design: The study was prospective descriptive, cross sectional and observational. Place & Duration of Study: The study samples were collected during the months of April and May 2005 at the out patient department of The Children's Hospital & the Institute of Child Health, Ferozepur Road, Lahore. The biochemical analysis was carried in the Biochemistry laboratory of the Post Graduate Medical Institute, Birdwood Road, Lahore. 90 Materials & Methods: A special research instrument and exclusion, inclusion criteria were designed. The infants up to the age of 1 to 6 months were selected in three groups, each of sixty infants, taking mother's milk, infant formula and fresh milk. The mothers were requested to participate in the study and after the consent 2 cc venous blood sample