The process of urbanization in the Third World has vastly outstripped the equivalent change in industrialized countries, and also far exceeds the population growth. This urbanization has been associated with the spread of artificial feeding and associated short birth intervals. Although relatively few studies have been undertaken on the effect of length of birth interval, we have good evidence that it is associated with poorer growth, a less satisfactory intellectual development, and a higher mortality. Child health programmes have, up to the present, been only marginally involved in the question of birth interval, although as mentioned this has a considerable effect on the health of the child. In overcoming malnutrition, simple weight charts are now widely accepted as a useful tool by which the adequate growth of the child can be monitored, and in this way malnutrition prevented. These same weight charts can be a useful means of identifying in any community the month in which a woman has a 5% chance of conceiving again. The charts can also be used as a means of recording the dialogue between the health worker and the parents on the most appropriate time interval to separate their children. However, to achieve this the developing countries will need a vast increase in the health personnel they have available. Experience now in a number of countries suggests that the part-time health worker may be particularly appropriate for providing such services.