Background: Protein-calorie malnutrition (PCM)disturbs profoundly the functions of the immune system, especially the cellular type immune response.In order to find the immunological criterion of malnutrition severity and effectiveness of realimentation, the reported first phase of the study attempted to assess quantitatively the phenotypic characteristics of peripheral blood lymphocytes and to test the correlations between serum Il-12 levels and the counts of specific lymphocyte subpopulations in blood of children with PCM. Material/Methods: In 50 children with PCM, subjective and objective examinations were performed and somatic development assessed.All the children underwent routine blood count tests and determinations of CD19+(LB),CD3+(LT),CD4+(LTh), CD8+(LTc/s), CD3HLADR+(active LT)and NK cells (CD56)population counts performed using monoclonal antibodies and flow cytometry. Additionally, serum Il-12 levels were determined by ELISA.Results: Malabsorption syndrome was the most common cause of malnutrition in the examined children. Both body weight and body mass indices (BMI) of 49 children were below the 3 rd percentile and in 1 child –between the 3 rd and 10 th percentile. Although total blood lymphocyte counts were decreased in 19 children (38%)only, cytometry demonstrated reduced populations of LB in 56%, LT in 52%, LTCD8+in 56%, LTCD4+in 36%, LT HLADR+in 74%and NK cells in 62%of children.Serum IL-12 levels ranged from 8.78 pg/ml to 242.36 pg/ml (x –130.93 pg/ml)and demonstrated a statistically significant positive correlation with the number of LT and the counts of their specific subpopulations (r=0.41 –0.54, p

Keywords: protein-calorie malnutrition, children, lymphocyte subpopulations, IL--12