The influence of plant growth regulators, sucrose, calcium and various macronutrient media on callus friability and somatic embryogenesis was investigated inHevea brasiliensis Mull. Arg. Friable and embryogenic calli were spontaneously formed in two rubber tree clones (PR 107 and RRIM 600) on the Medium for Hevea (MH), with 3,4-dichlorophenoxyacetic acid (3,4-d), kinetin and sucrose, while compact embryogenic calli were enhanced in three other clones (PB 260, PB 235 and GT1). Callus friability was enhanced in clone PB 260 when the concentration of one growth factor (3,4-d or kinetin) was reduced from 4.5 μLM to 0.45 μM during the first culture, or when high sucrose or calcium levels 351 mM and 12 mM, respectively) were maintained during subcultures. The different macronutrient media did not alter callus texture but only use of MH and Murashige and Skoog (MS) media led to somatic embryogenesis. Friable calli obtained by modifying the auxin/cytokinin balance lost their embryogenic potential. In contrast, those obtained on media with high sucrose or calcium concentrations were mainly composed of embryogenic cells embedded in a mucilaginous matrix. Such calli could be of potential interest for establishing embryogenic cell suspension cultures.