The present invention relates generally to a method of modulating cellular activity and to agents for use therein. More particularly, the present invention provides a method of modulating the level of sphingosine kinase functional activity. In a related aspect, the present invention provides a method of modulating sphingosine kinase mediated signalling via modulation of its intracellular level of activity. The present invention still further extends to novel molecules which exhibit the capacity to induce sphingosine kinase activity. The methods and molecules of the present invention are useful, inter alia, in the treatment and/or prophylaxis of conditions characterised by aberrant, unwanted or otherwise inappropriate cellular functional activity and/or aberrant, unwanted or otherwise inappropriate sphingosine kinase mediated signalling. The present invention is further directed to methods for identifying and/or designing agents capable of modulating the level of sphingosine kinase activity.