Functional, metabolic and molecular studies using purified beta cells (β-cells) have contributed to our understanding how insulin synthesis and release are regulated by glucose. Individual rat islet β-cells are heterogeneous in their threshold sensitivity to glucose, so that the physiological graded glucose-induced response of the pancreatic β-cell population can be explained – at least in part – by dose-dependent recruitment of cells. β-Cell threshold sensitivity to glucose is correlated to glucokinase gene expression rather than glucose transport, reinforcing the concept that glucokinase is directly involved in β-cell glucose sensing. This idea is further supported by observing major species differences in islet GLUT2 expression, whereas islet cell glucokinase expression and function are strongly conserved. Studies on pure rat β-cells have also shown that cyclic AMP acts – in addition to its well-known potentialtor function of glucose-induced insulin release – as a competence factor which is absolutely required for normal β-cell responsiveness to glucose. Intraislet glucagon appears to be a paracrine regulator of cyclic AMP production in vitro, but this signalling pathway can be an artifact of the islet isolation procedure. In rat β-cells, expression and functional activity can be demonstrated of receptors recognising glucagon, glucagon-like peptide 1 and glucose-dependent insulinotropic peptide. Whether this diversity in signalling reflects another form of β-cell heterogeneity, functional complementation or biological redundancy, remains to be investigated.