An inoculum containing two amylolytic and three cellulolytic thermophilic bacteria, isolated from a preceding compost pile and identified as Geobacillus species by 165 rRNA gene sequencing, was applied to a mixture of market waste, rice straw and cow dung (5:1:0.2) so that the initial cell density was 2 x 10(8) colony forming unit (CFU) per gram dry weight at 55 degrees C. The inoculation increased the total cell count particularly in the thermophilic stage as determined by flow cytometry. Concomitantly, there was a significant rise in microbial metabolism in the compost pile as reflected by the dehydrogenase activity. As a result, the C/N ratio dropped more rapidly in the inoculated mixture than that in the control without inoculum. The study, therefore, suggested that inoculation by thermophilic bacteria would be effective in the composting process at least in the thermophilic stage. (C) 2009 Elsevier Ltd. All rights reserved.