In one set of simulations, based on epidemiological data from rural Uganda, it was demonstrated that a combined biomedical and behavioural intervention which (a) increased condom use in contacts between men and casual sex partners to 50%, (b) reduced the frequency of these contacts by 50%, and (c) reduced the average duration of STD episodes by 50%, could reduce HIV incidence by 50% in the first year and 80% over ten years. Empirical studies have shown that changes of this nature are possible and can lead to large reductions in HIV incidence. In Nairobi, health education and condom promotion led to an increase in condom use among commercial sex workers from 8% to 66%. Condom use was associated with a 3-fold reduction in risk of sero-conversion [17]. In Zimbabwe, large-scale condom promotion programmes were associated with 48% and 53% reductions in STD cases over three years, in Bulawayo and Mutare, respectively. Most of these reductions were achieved within the first year of the intervention [18]. In a study of 752 male factory workers in Mwanza, Tanzania, counselling at an STD clinic contributed to significant reductions in reported high-risk behaviour - eg: the proportion with more than one sexual partner in the preceding month fell from 22% to 12% - and a large (63%) - but non-significant - reduction in HIV incidence [19,20]. In a randomized control trial in rural areas around Mwanza, improved diagnosis and treatment of STDs was associated with a 42% reduction in the incidence of new HIV infections over a two-year period [21,22].