In order to develop a more efficient genetic transformation system for cacao somatic embryos, the effects of polyamines and b-lactam antibiotics on somatic embryogenesis, hygromycin as selective agent, and different factors affecting uidA gene transfer have been evaluated. The polyamines putrescine, spermidine, and spermine significantly improved secondary somatic embryogenesis in cacao. Spermine at 1,000 lM provided the best responses, increasing 6.79 the percentage of embryogenic callus and 2.59 the average number of embryos per embryogenic callus. The b-lactam antibiotics timentin and meropenem, used for Agrobacterium tumefaciens counter-selection, had a nondetrimental effect on secondary somatic embryogenesis, depending on their concentration, whereas the commonly used b-lactam cefotaxime inhibited it, irrespective of the tested concentration. Hygromycin showed a strong inhibitory effect on secondary somatic embryogenesis of cacao, impairing completely the embryo production at 20 mg l -1 . Following the criterion of GUS activity, the best conditions for T-DNA transfer into cotyledon explants from primary somatic embryos of cacao were a sonication of the explants for 100 s, a 20-min incubation period in Agrobacterium solution, an Agrobacterium concentration of 1.0 (OD 600 ), and cocultivation of the explants on tobacco feeder layers. These findings will have important implications for studies on functional genomics of cacao.