together with short communications from members to In 1972 the 10th Annual Symposium of the Society for the provide a valuable overview of the current status of this Study ofInborn Errors of Metabolism was held in Cardiff field. The difficulty in establishing an uneq uivocal clinical and the proceedings published in 1973. The meeting was devoted to the treatment of inborn errors of metabolism; response to vitamin treatment was discussed by Dr in particular the dietary treatment of phenylketonuria Leonard. The papers on biotin-responsive combined and vitamin responsive disorders were reviewed. These carboxylase deficiency presented by Drs Bartlett, Wolf two areas have seen notable advances in the intervening and Baumgartner emphasized the widely differing years. It has become apparent that a number of variants of mechanisms which may underline apparently similar PKU are due to defective cofactor metabolism, and, clinical responses. In particular biotinidase deficiency appears to be a unique defect of cofactor recycling. indeed, some patients refractory to simple dietary restriction of phenylalanine respond to the adminis- Riboflavin, thiamine, and pyridoxine responsive disor- tration of the phenylalanine hydroxylase cofactor ders were succinctly reviewed by Drs Gregersen, Duran and Fowler, again interspersed with relevant short biopterin or related compounds. Biopterin, normally communications from members. Two papers by Drs synthesized de 110W, in some individuals has become a -vitamin'.