The effect of exogenous ethephon and its combination with gibberellic acid (GA3), indole-3-acetic acid (IAA) and benzyl amino purine (BAP) on tension wood formation in the vertically growing shoots of Leucaena leucocephala has been studied using light and scanning electron microscopy (SEM). The application of exogenous ethephon induced tension wood formation. The percentage of tension wood severity in the shoots was directly proportional to the concentration of ethephon applied. SEM studies revealed the replacement of S2 and S3 fibre wall layers with the gelatinous layer (G-layer) in response to high concentration of ethephon. Ethephon exhibited synergistic interaction with GA3 and BAP in tension wood formation. Fibres and vessel elements in tension wood, induced by ethylene and its combination with other hormones showed increase or decrease in their dimensions irrespective of their concentration and combination. The density of rays increased in all the treatments except in the combination of ethephon and IAA. The anatomical data indicate that ethylene plays a major role in tension wood formation and it interacts synergistically with gibberellins and cytokinin. On the other hand, such synergistic interaction was not found between ethephon and IAA in tension wood formation.