For many species recalcitrance is still a problem when attempting to propagate plants by in vitro culture, especially when explants from adult individuals are used. In spite of extensive experimentation with variations in growth regulator concentrations and combinations, nutrient components and other factors commonly studied, efforts to propagate plants in vitro still often fail. This review looks at the possibilities of using gaseous growth regulator compounds in attempts to overcome such recalcitrance. The gaseous growth regulators most studied are ethylene and nitric oxide and the focus of this review will be on these. Less is known about carbon monoxide and hydrogen sulfide. These also have distinct morphogenetic effects and could perhaps sometimes be of use in solving recalcitrance problems.