Assessment of serum protein concentrations in protein-calorie malnutrition was carried out by two specific immunochemical methods, the Single Radial Immunodiffusion technique and the Automated Immunonephelometric procedure. The correlation coefficient (r) between the two methods was above 0.85 for all the serum proteins assayed. The automated nephelometric assay procedure has the advantages that it is rapid and that a large number of samples can be readily processed. The system in its present form could not be readily used to quantitate proteins such as prealbumin whose serum concentration was less than 50 mg/100 ml. The single radial immunodiffusiton technique gave more consitent results for IgA estimation than the automated technique. With the exception of C4 and the immunoglobulins, all the serum proteins assayed were lower in children with protein-calorie malnutrition than in control children. During refeeding in children with protein-calorie malnutrition the first serum protein to show a significant rise was C3. This was followed by transferin, then prealbumin and lastly albumin. C4 did not show any significant change. In experimental protein-calorie malnutrition in rats, the first serum protein to show a significant reduction was C3. This was followed by transferrin and then albumin. On refeeding the rats these serum proteins returned to normal values in the same order.