Jet lag is a temporary sleep disorder among air travellers who rapidly travel across time zones. Jet lag occurs as a result of the slow adjustment of the body clock to the destination time. Melatonin is a hormone which is responsible for sleep-wake- cycle which is secreted by pineal gland and are stimulated by darkness and suppressed by light.Melatonin secretion increases up to 10-fold during the darkness of night and then fall to low levels during the light of day. Melatonin levels are higher in children and decline with age in adult. So melatonin is the hormone which is responsible for this biological system discomfort.