The primary purpose of this research is to provide insight into how to reduce the rising rate of HIV infection among men who have sex with men (MSM) in Canada. The number of HIV infections in Canada continues to rise annually, with MSM accounting for a disproportionate number of these new infections. Evidence now suggests that individuals are highly infectious during the early stage of HIV infection, and these individuals are responsible for generating 11 to 40% of new infections annually. Indentifying individuals as soon as possible after acquiring HIV infection and providing a risk reduction intervention is necessary to curtail this HIV epidemic among MSM. Traditional HIV antibody testing is unable to detect HIV during this early infective stage; a new technology (nucleic acid amplification test-NAAT) that can identify early HIV infection has recently become available and will be used in this study. Traditional epidemiologic methods have focused on individual-level risk factors (e.g. number of sexual partners, condom use) but these have failed to fully explain transmission dynamics or control epidemic growth. Social network analysis (SNA) is a methodology that considers relationships, and interactions among those with varying risk characteristics in the social context. SNA is increasingly being applied to infectious disease epidemiology and research suggests this is a useful approach to the study of HIV transmission dynamics. MSM who acquire HIV are likely to belong to social, sexual, and drug-using networks whose members have similar risk behaviours. We hypothesize that early HIV detection and risk reduction interventions targeting these individuals, and their networks, will reduce the transmission of HIV. This research will employ SNA to examine and describe the social, sexual, and drug-using networks of MSM diagnosed with early HIV infection using NAAT. Network information will be used to identify networks containing high levels of risk behaviour and networks with a high incidence of early HIV infection. An enhanced prevention intervention will be developed with MSM community participation and implemented among individuals within the network who are engaging in high risk behaviour, and who are prominent in the network. In addition, SNA will be used to evaluate how the networks change over time (post-intervention) considering network structure, sexual mixing patterns, rate of partner change, risk behaviour, and to determine forward HIV transmission events.