Data were colleted on the scent-marking patterns of radio-collared and visually identifiable tigers for 4 years in Royal Chitwan National Park, Nepal. Five categories of marking were recorded: urine spraying; scraping with deposits of urine faeces, and anal gland secretions; clawing; cheek rubbing; and vegetation flattening. Urine spraying and scraping were the predominant forms of marking in this population. Tigers marked more heavily at territorial boundaries than in the interior of territories. Furthermore, in border areas marks were highly clumped at contact zones where major routes of travel approached territorial boundaries. This pattern appears to be a result of the density of vegetation which channels travel. The intensity of marking in these zones represented a higher frequency of marking rather than an increase in time spent in these areas. Marking was most intensive when tigers were establishing territories, and animals on adjacent territories appeared to mark in response to each other. Females marked intensively just prior to oestrus; this behaviour was reduced during oestrus. Males marked more frequently when females were in oestrus than during other stages of the females' cycle. A model is proposed where an odour field signals the risk of encountering a conspecific, thus allowing animals to compare the costs of possible encounters with the benefits of use of a given area.