The production of melatonin by the pineal gland and its functions are considered, and then its possible uses in the treatment of children. Institutionalized children, and those with severe learning disorders, often have irregular sleep-wake patterns, and there is evidence that melatonin can result in improvement to the benefit of both the child and the carers. The affected children can become less irritable, calmer, happier, and content. Also they may socialize better and become more attentive, with an improvement in their cognitive abilities. Another group of children who are likely to suffer from disturbed sleep are those who are visually handicapped. Melatonin given in the evening can improve their sleep patterns, and often their performance. No important side-effects have been reported. It is generally accepted that if a child is liable to epileptic seizures sleep deprivation may well exacerbate them. There is some evidence from clinical trials that in that event melatonin can be helpful. There are many other problems in which it is claimed that treatment with melatonin is justifiable. These are mentioned, but further confirmatory studies are needed in most of them. There is no doubt that melatonin can effect the circadian system, and shift the sleep-wake cycle; and that there are situations in which this can be desirable.