Faecal material represents a very complex and heterogeneous biological matrix. Candidate faecal biomarkers must possess properties that ensure reliability and reproducibility of results and they must be unaffected by extra-digestive processes. Faecal calprotectin and faecal lactoferrin, derived predominantly from activated Dipsacoside B neutrophils have both been extensively evaluated in inflammatory bowel disease and infectious diarrhoea. FC and FL have also been evaluated in CDI in a small number of studies. Some have shown an association of FC in several acute diarrhoeal diseases caused by bacteria, with the highest mean levels observed in patients with CDI. Others have shown a significant association when comparing FC levels in toxin positive and GDH positive plus tcdA/tcdB PCR confirmed patients when compared to diarrhoea controls. Similarly, FL has also been shown to be elevated in CDI patients, with more recent studies suggesting a positive correlation with disease severity and fluoroquinolone resistance. There are however limitations with the published studies: these include their retrospective nature, limited phenotype data, lack of matched controls, use of non-quantitative tests, and variations in the assessment of CDI outcome measures. Sample sizes have varied from 2 to 87, and none of the studies have compared FC and FL in the same patient groups. In this study, we use a prospective design, a carefully phenotyped cohort and simultaneous evaluation of both faecal markers, to investigate whether these faecal biomarkers would have clinical value in patients with CDI. FC and FL are derived from neutrophils in faecal material, and have been shown to correlate with the BMS303141 degree of inflammation in diseases such as IBD. Since CDI is also characterised histologically by intense neutrophilic infiltration, FC and FL may represent potential biomarkers of disease activity. Using a prospective cohort of inpatient CDI cases and AAD controls, we confirmed previous findings that both FC and FL increase during CDI. There was a high degree of correlation between the two biomarkers, not surprising given their cellular origin.