Default rates are series commonly used in stress testing. In Canada, as in many other countries, there are no historical series available for sectoral default rates on bank loans to firms. Knowledge of such data is required to assess the impact of shocks on the balance sheets of financial institutions and to conduct stress-testing exercises of the banking system. The authors discuss the methodology used to construct historical series of firm default rates for selected sectors of the Canadian economy, as well as the models applied to predict default rates. Their findings confirm the existence of a non-linear relationship between the gross domestic product, the unemployment rate and default rates.