This series of papers is presented as a tribute to Wilfred F. Widdas, Emeritus Professor, Bedford and Royal Holloway College, University of London. The papers are the outcome of a meeting held by the Physiological Society on January 5th 1997 at Sheffield as a celebration of Widdas's scientific work. The work referred to of course is the series of papers by Widdas and co-workers describing mediated transfer of sugars across cell membranes. The ideas therein relating to carrier-mediated transport of sugars across membranes have become one of the most influential scientific paradigms in modern biology. The history of science shows that a successful paradigm has its supporters, who work either to extend its influence to ever wider spheres, or to understand the nature of its constraints. The natural tendency is for this support group to diminish the importance of anomalous results; this consequently breeds an opposition group whose aim is to show that these anomalies require major adjustments to the paradigm. This arrangement leads to the formation of scientific factions and eventually either to the overthrow of the paradigm or to a major reconstruction and thus scientific advances. A special feature of sugar transport is the relative scientific longevity of the workers in the field, of whom Widdas is a prime example; a similar tendency was found in quite a few of the participants at the meeting. Another is that they do not fall easily into the facile categories of supporters or adversaries of the carrier paradigm. Although Wilfred Widdas's early work led both to the formation and refinement of the carrier molecule, he always has had a more open view about the nature of the transporter than many of its more ardent supporters. His indefatigable scientific curiosity has led him to investigate some nagging anomalies in the theory of glucose transport and consequently somewhat away from the mainstream. This rare and courageous stance stems, perhaps, from the Non-Conformist tradition from which he comes and certainly demonstrates a monumental dedication to science. All the participants are grateful to the Physiological Society and Glaxo-Wellcome for their financial support and the editors of Experimental Physiology for their help in testimonial publication.