Chlamydia trachomatis and Neisseria gonorrhoeae are the two most frequently occurring bacterial sexually transmitted diseases (STD) in Canada. The burden and costs of both diseases are primarily due to the sequelae which include pelvic inflammatory disease, ectopic pregnancy and infertility. Although preventive programs have been largely successful at reducing the number of cases in the last two decades, a decrease in disease is no longer evident. If gonorrhea is to be eliminated and chlamydia incidence greatly reduced in Canada, new control strategies need to be implemented. STD epidemiology is dominated by the concept that a small subset of the population known as the "core group" is essential in maintaining the endemicity of STD in a population. Through high numbers of partners, and long periods of infectiousness, core group members contribute disproportionately to STD spread. Mathematical formulae have been used to prove core group theory the equations have seldom, if ever, been solved. The goal of thisresearch was to define predictors for members of chlamydia and gonorrhea core groups using the mathematical equations. The proposed core group populations comprised individuals repeatedly infected with chlamydia, gonorrhea and with both organisms, and multiply named sexual contacts of cases from 1990 through 1992. After substituting infection transmission probabilities and duration of infection estimates from the literature, and partner change rates from this research the results of the mathematical equations formulae strongly suggest that the proposed core groups do indeed encompass the true core groups. They also show that in a population with a high incidence of gonorrhea, and where dual therapy for both gonorrhea and chlamydia is practiced, combination therapy for chlamydia is effective and chlamydia will become a non-viable infection. Last, the feasibility of constructing sexual networks from contact data for the purposes of better defining core groups was successful, and revealed an astonishingly large network of more than 900 connected people, the upper limits of which are still to be established. Future investigation into the uses of social network analysis for both practical use by field staff and for the understanding of STD epidemiology is essential.