This review considers recent studies on the role of plasmodesmata in the conduction of small solutes and signalling molecules between plant cells. The substructure of plasmodesmata is described in relation to the potential pathways available for symplastic signalling between cells. At least two discrete pathways are available for transport through plasmodesmata, the cytoplasmic sleeve between the desmotubule and the plasmalemma, and the endoplasmic reticulum which connects contiguous cells via the central desmotubule. This latter pathway has been shown recently to function as a dynamic continuum for the movement of lipids and lipid-signalling molecules between plant cells. The role of plasmodesmata in the conduction of hormones and electrical signals is also considered, as is the potential for movement of macromolecular signalling molecules via the symplast. The factors which regulate plasmodesmatal conductance and the significance of symplast 'domains' are discussed in relation to the control of movement of signalling molecules in the symplast.