OBJECTIVE Mexican legislation considers many public places as smoke-free spaces. However, no environmental tobacco smoke exposure assessment studies exist to evaluate compliance with governmental regulations and to identify opportunities for tobacco control. The main objective of this study is to quantify airborne nicotine concentrations in public places in Mexico City. METHODS During March 2004, nicotine passive monitors were allocated in a hospital, two schools, a public office building, an airport, seven restaurants, and three bars following a common protocol applied in other Latin American countries. Monitors were analyzed at the Johns Hopkins University, extracting the nicotine and quantifying it using nitrogen selective gas chromatography. Median concentrations of environmental nicotine were estimated by type of place and smoking restriction. RESULTS Airborne nicotine was detected in all public places. The highest concentrations were observed in bars (6.01 microg/m3), restaurants (0.69 microg/m3), airport (0.21 microg/m3), and public offices (0.10 microg/m3). Nicotine exposure concentrations are similar to those previously observed in other capital cities of Latin America. CONCLUSIONS Nicotine levels in the airport and public offices reflect the lack of compliance with mandatory non-smoking official regulations in Mexico. High nicotine concentrations in bars and restaurants provide evidence for the need to advance smoke-free legislative action in these public and work places.