The molecular discs around Young Stellar Objects can be detected through high spatial and spectral resolution observations of their position-velocity diagrams. By mapping a high lying transition of a density-tracing molecule (e.g. HON, HCO+, NH3), the lines should be optically thin and we can expect to see the signature of rotation of the protostellar accretion disc. We present single-dish observations of the S106 system which show evidence for the presence of such a rotating disc. We also discuss a simple disc model which predicts the form of the resulting 1-v diagram. With high quality data, we should be able to do the inverse problem that of recovering the disc properties from the 1-v diagram. We discuss approaches to this inverse problem both by a Singular Value Decomposition (least-squares) method, and by a Maximum Entropy Method.