Social networking sites (SNS), and especially Facebook, have revolutionised patterns of language and communication. We conducted a study to examine gender differences in language use on Facebook, by surveying 600 undergraduate students (388 females and 207 males), and analysing males' and females' responses to two Facebook status updates. There were a number of gender differences in terms of public replies to Facebook status updates. Females were significantly more likely to 'Like' a Facebook status update than males, post a public reply to a Facebook status update than males and show higher levels of emotional support than males. In contrast there were hardly any gender differences in terms of sending private messages in response to Facebook status updates. There was no gender difference in terms of level of emotional support in private messages. Females were more likely to send a private message than males, but this difference was very small. The implications of these findings for explanations of gender differences in language are discussed.