The optimization of regeneration protocol for different genotypes increases the yield in transformation studies. Cotyledon explants of watermelon [Citrullus lanatus (Thunb) Matsum & Nakai] cv Crimson Sweet were cultured on MS medium containing combinations of benzyl adenine (BA) (0, 5, 10, 20 muM) and indole-3-acetic acid (IAA) (0, 0.5, 5 muM). Maximum shoot growth and subsequent rooting from explants on regeneration medium were obtained from the media containing 10 muM BA + 0.5 muM IAA and 20 muM BA (75 and 78%) by direct organogenesis, respectively. Histological analysis showed that cell division was observed in the epidermal and subepidermal layers. Protuberant structures were observed in tissues between 7 and 12 days in culture. Meristematic structures were observed after 12 days in culture which later developed into buds.