Background: The use of coca paste also used in Bolivia, Colombia, Chile, Perú and Uruguay, has increased in Buenos Aires in the last decade. Coca paste is an intermediate step in the manufacturing process between coca leaves and purified cocaine. Changes in the drug market together with the economic and social crises in Argentina seem to have created a coca paste outbreak, estimated by different studies from the National Drug Control Agency. A study upported by the Pan American Health Organization (HSS/RC/ARG-3320-PAHO/WHO), estimated HIV, Hepatitis B, C (HBV and HCV), and Syphilis seroprevalence among current coca paste users in Buenos Aires.Methods: A descriptive, cross-sectional study among 170 current coca paste users (never injectors) was conducted between Nov2006/Nov2007. 78% individuals were recruited in drug treatment centers and 22% in the neighborhoods were they live. Informed consent, a structured questionnaire and serological diagnosis, counseling and Hepatitis B vaccination were carried out. Results: Sample was 85% male, mean age: 26 years old. Mean years of formal education: 10, which is a lower level of education compared to the general population (p<0,005). Unemployment: 29% in most of the last year.Coca paste users referred: 22.4% of pulmonary complications, 70% injuries in the mouth, and 67.6% loss of more than 10kg of weight. Seroprevalence was: HIV 2.9% (CI95%1.0-6.4), syphilis 2.4% (CI95%0.7-6.3), HCV 2.4% (CI95%0.7-6.3), HBV: HBcAb 3.5% (CI95%1.4-7.9). One person had acute Hepatitis B (HBsAg+, HBcIgM +, HBeAg+). Co-infections were: HIV/HCV: 40% (2/5), HIV/Syphilis: 20% (1/5), HIV/ HBcAb: 40% (2/5). Conclusions: Young men with a low educational level and a high rate of unemployment compraised the majority of the sample. The observed rate of infections, health care problems and co-infections found indicate the need of addressing coca paste users with specifically oriented harm reduction strategies, considering the impact of this drug use trend in several countries of Latin America.