The early development of bar-gnawing was studied in young gerbils kept in standard laboratory cages. Bar-gnawing was performed on the bars of the cage lid and developed shortly after eye-opening at an age of 18 days. It increased in bout length and duration with age and there was considerable variability in behaviour between individuals. It is discussed as to whether bar-gnawing is a stereotypy and in which behavioural context it develops.