PIP: Protein energy malnutrition (PEM) continues to be a major public health problem in Thailand. It affects physical growth, mental development, learning ability, and immune response to infections. In this discussion of PEM related to diarrhea in the children of Thailand, attention is directed to the following: intrauterine malnutrition; the practice of breast feeding; the prevalence of PEM in the early infancy period; the prevalence of PEM in preschool children; diarrhea in infants and children; and possible solution to the problem of PEM and diarrhea. For some infants, PEM occurs during the intrauterine period. In the urban slum areas of Bangkok where breast feeding practice was about 34-45%, the prevalence of PEM based on weight for age was very high among infants under 6 months of age. 3rd degree PEM in the 2 urban slum areas was 13 and 17% as compared to 0% in the semi-rural area of Bang-Pa In, where breast feeding practice was about 62-65%. The total prevalence of PEM in the urban-slum areas ranged from 71-79%, which was approximately 3-4 times that of the semi-rural area. The decline of breast feeding practice, the improper handling and unhygienic preparation of artificial feedings are the major contributing factors to PEM associated with diarrhea during early infancy. The prevalence of PEM among preschool children in Thailand during 1979-1980 was approximately 56% with 39.5, 14.2 and 2.3% of 1st, 2nd, and 3rd degree respectively. The highest prevalence of PEM was observed in preschool children of the northeast which has been considered the poorest region in the country. Diarrheal disease has been for many years the 1st or 2nd leading cause of death in Thai infants. Infants and children who are suffering from moderate and severe diarrhea will result in high mortality and morbidity attributable to PEM. In 1 report, all infants with intractable diarrhea were malnourished, 70% of them were classified as 3rd degree PEM and 15% each were 1st and 2nd degree PEM. The interrelationship between PEM and diarrhea in infants and children is now recognized as the most critical health problem of the developing countries. In an effort to improve the nutritional status of infants and children by alleviating PEM and diarrhea, the National Economics and Social Development Board has developed a set of food and nutrition policies in the 5th National Plan during the period from 1982-1986. Major emphasis will be on parent education in maternal nutrition, infant feeding, and hygienic handling and preparation of food for infants.