At the time of protrusion, radicles of lettuce seeds became susceptible to desiccation damage. Concomitant with radicle elongation, both the reducing sugar content and the amount of lipid-aldehydes increased. The role of the hydroxy- and lipid-aldehydes in browning reactions that occurred during desiccation and re-imbibition was analysed. It was concluded that both types of aldehydes reacted with amino-groups during desiccation and that the increase in lipid-aldehydes during germination could be due to the augmented reducing sugar content. Therefore, the high reducing sugar content in radicles of germinated lettuce seeds may be the primary source of hydroxyl radicals, and thereby, a principal cause of desiccation damage.