The purine derivatives (PD) have been proposed as a non-invasive method to estimate microbial-N supply to the small intestine (Chen et al., 1990a; Verbic et al., 1990). The use of PD urinary excretion has the advantage that it can be used with intact animals thus reducing the concern of animal welfare issues. Although, there are known differences in purine metabolism between cattle (B. taurus), sheep and buffaloes (Bubalis bubalis) (Chen et al., 1990b; Chen et al., 1996), no direct comparison of PD urinary excretion has been made so far between cattle especies, therefore, the objective of the present experiment was to compare PD urinary excretion of B. taurus and B. indicus cattle fed similar diets under tropical conditions.