Hydrogen sulfide (H2S) is now considered to be a signalling molecule in a range of organisms. In animals and plants there are characterised mechanisms for its generation and removal suggesting that it can be made and have an effect when required. In plants H2S has been found to help mediate a host of physiological events, from seed germination to flower senescence. Furthermore, H2S has been found to be involved in a range of stress responses. What is clear, however, is that such physiological events and responses also involve reactive oxygen species (ROS) and nitric oxide (NO), and therefore considering the mechanisms by which H2S has its actions requires that interactions with other reactive molecules must be taken into account. H2S may be able to a have effects on the enzymes involved in ROS and NO accumulation, or H2S may have a direct reaction with ROS or NO. Furthermore, ROS, NO and H2S are all able to partake in the modifications of thiol groups, suggesting that the final outcome will be dependent on the concentrations and locations of molecules such as ROS, NO and H2S. It has been suggested that one of the ways in which H2S may have its effects is in the modulation of ROS and NO metabolism, keeping it in check until required to relay a signal. What is clear is that future work needs to consider all these reactive compounds as a group, to unravel how they truly interact and bring about a co-ordinated response.