Serum magnesium levels were measured by atomic absorption spectrophotometry in 46 malnourished and 12 healthy children, aged 3 months to 5 years. The nutritional status of children was classified in relation to weight for age and height for age using the Indian Academy of Pediatrics and the Waterlow classifications, respectively. NCHS data were used for the purposes of comparison. Serum magnesium levels were significantly low in children with moderate (weight for age 61-70 per cent) and severe (weight < or = 60 per cent) malnutrition, and in children with marked linear growth retardation (height for age < 85 per cent). Nearly half of the marasmic children had serum magnesium levels in the hypomagnesemic range (below 1.56 mg/dl). Serum magnesium levels had significant correlations with height for age and serum albumin.