The effects of damage to the main stem apex of the cotton plant caused by feeding of Lygus vosseleri Popp. have been investigated using a cell counting technique. It was found that mechanical damage of the tip due either to feeding of Lygus or to pricking with a glass needle caused an increase in cell division and maturation rates in the stem apex. The significance of this in relation to the possible effects of Lygus damage on plant height is discussed.