The colonic separation mechanism in lagomorphs and some rodents, associated with caecotrophy, serves to retain microbial protein. As tropical fruits have low protein concentrations, caecotrophy could be an important microbial protein source in frugivorous rodents such as the paca (Cuniculus paca). Due to conflicting reports on the occurrence of caecotrophy in this species, we obtained digestive tracts of three adult animals and observed the behaviour of four specimens maintained on a diet of a pelleted feed (P) and a supplemental mix of fruits and sweet potato (S, a source of structural fibre). In a Latin square design, P and S were both offered either in the morning (M) or in the afternoon (A), or with one item in the morning and the other in the afternoon (SP or PS). The paca's proximal colon is characterized by a distinct furrow typical for the colonic separation mechanism of hystricomorph rodents. Caecotrophy, both "direct" (from the anus) and "indirect" (from a pile of defecated faeces), was a regular component of the paca's behavioural repertoire, and caecotrophs contained more nitrogen and less fibre than hard faeces. Higher food intake led to less overall caecotrophy. With afternoon feeding of S, the onset of caecotrophy was delayed and the proportion of indirect caecotrophy increased, with hard faeces and caecotrophs often defecated together. No indirect caecotrophy occurred on treatment M. The results suggest that the time available after ingestion of structural fibre determines the efficiency of the colonic mechanism for the separation of hard faeces and caecotrophs.