To study the effect of pineal extract of camel and or pineal active substances melatonin and serotonin on somatic growth, forty newly born rats were divided into four groups, ten animals each (three experimental and one control). The experimental groups were daily injected with either pineal extract, serotonin or melatonin, starting from day 2 postnatally up to the 28th day. The weights of the inject ed groups were all reduced below the control values and the decrease was highly significant. To test, if the reduction was due to a matabo lic factor or undernutrition, the perineurial barrier was examined by a HRP tracer technique. All experimental animals showed a normal intact barrier function like the control. This means that those animals were not subjected to undernutrition and the cause of weight reduct ion may be a metabolic factor related to growth hormone.