The root-promoting ability of water extracts made from gelling agents (agar and Gelrite) was investigated using the mungbean rooting bioassay. Autoclaving these water extracts decreased the number of roots in mungbean cuttings compared to the controls. The addition of activated charcoal to the water extracts from Agar Bacteriological and Agar Commercial Gel had no effect on their root-promoting ability. Extracts with exogenous indole-3-butyric acid (IBA) which were treated by autoclaving or via a freeze-thaw cycle, significantly increased rooting. However, incorporation of activated charcoal to similar IBA-contaming extracts reduced rooting. Our results indicate that more attention should be given to the choice of gelling agent and its interaction with other additives in the media used during tissue culture. (c) 2005 Elsevier Ltd. All rights reserved.