volatile fatty acids were implicated as foot malodorants, with isovaleric acid particularly prominent. l-Leucine was identified as the likely substrate, and the source of this branched amino acid postulated to be the degradation of foot callus. An in vitro assay was employed to screen a library of isolated foot bacteria for their ability to generate isovaleric acid from l-leucine. Staphylococcus species were found to be the main producers, while some Brevibacterium, Micrococcus and Kytococcus isolates fully catabolized isovaleric acid and l-leucine, indicating the dynamic nature of odour production.