The present study examined communication among males and females participating in Internet support groups. Previous qualitative research on Internet support groups has suggested that female cancer patients exhibit higher levels of emotional expression than males, and male cancer patients use Internet support groups for information exchange. We developed a laboratory-based protocol for investigating gender differences in online communication, testing the hypothesis that preparation for the online groups would increase levels of disclosure. One hundred and sixty-seven undergraduates were enrolled in same-gender support groups to discuss the shared experience of having a loved one with cancer. Participants were randomized to one of three preparation groups: minimal instruction, detailed instruction with social modeling, and detailed instruction with social modeling and practice. Linguistic Inquiry and Word Count was used to measure levels of emotional and cognitive expression in messages sent to the group. Participants used increasing levels of emotional and cognitive expression over time; this pattern was not altered by preparation and did not differ between males and females. The levels of emotional and cognitive expression during Internet communication suggest that the Internet may be a viable medium for the provision of psychosocial services to people in need of supportive care, such as cancer patients. © 2003 Elsevier Science Ltd. All rights reserved.