In this thesis, the work undertaken in an attempt to gain insight into the location of the binding site of bilirubin is described. The history, properties and biosynthesis of both bilirubin and albumin are reviewed in Chapter One. Chapter Two contains an account of the novel one-step method of labelling bilirubin of high yield and specific activity. In Chapter Three, the effect of light on bilirubin in the presence and absence of albumin, followed by the labelling of the albumin in an attempt to obtain information regarding the nature of the amino acid residues involved in the binding of bilirubin to albumin. Attachment of labelled bilirubin to albumin enabled the possible site on the latter to be followed during degrading procedures. Possible effect of this photo-induced binding on phototherapy is described. Chapter Four contains an account of the synthesis and binding studies of mesobilirubin. Fluorescence and spectroscopic methods are employed to determine the association constants of mesobilirubin and comparison with bilirubin made. The importance of the vinyl groups in bilirubin binding is cited and the possibility of mesobilirubin being a kernicteric pigment is hypothesized.