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Agar and activated charcoal (AC) are commonly used in tissue culture. However, their deeper actions and functions are largely unknown. This experiment investigated the effect of agar and AC, singly and jointly, on gibberellin (GA) uptake by corn shoots. Corn seeds were germinated on Murashige and Skoog medium (MS). Shoot excised from 1-wk-old seedlings were cultured on liquid (0.0 g l−1 agar) or solid (8 g l−1 agar) MS containing 3 μM indole-3-acetic acid, 13.3 μM N6-benzyladenine, and 6000 CPM ml−1 [3H]GA4 as tracer. Both liquid and solid media had two treatments, one without AC and one supplemented with 5 g l−1AC. Uptake of [3H]GA4 and morphogenesis of corn shoots were recorded after 2 wk of culture. Corn explants cultured in AC-free media acquired high levels of [3H]GA4, while explants from AC-containing media showed only traces of [3H]GA4. Explants cultured in AC-free liquid medium contained about twice the amount of [3H]GA4 as those from AC-free solid medium. Addition of agar reduced shoot length, while addition of AC increased both shool and root length. It is concluded that: (1) agar reduced the uptake of GA4; and (2) GA4 was irreversibly adsorbed by AC, and thus became unavailable to corn explants.