Within the European research project VIR[FAB] (VIRtual FABrication of aluminium), a series of basic material testing has been performed on alloy AA3103 to derive constitutive equations for the simulation of hot rolling operations as well as to characterise the development of microstructure and texture under varying loads and temperatures. Alloy AA3103 is commonly used as core alloy for brazing sheets for applications in heat exchangers. The material was provided from industrial production and distributed to the different laboratories for testing. The material behaviour during hot deformation was analysed in plane strain compression, uniaxial compression, and hot channel die compression in the temperature range 250 to 500 degreesC and at strain rates of 0.1 to 100 s(-1) in the different participating laboratories. The data of the individual tests have then been evaluated according to standard procedures. Different constitutive models have been generated from the different sets of measured results. These models range from conventional empirical equations (flow stress as function of strain, strain rate and temperature) to more advanced physically based models (flow stress as function of microstructurally based variables of state). The quality of the fits is discussed together with the form of the constitutive equation. Finally, the effect of using different conventional constitutive models in the simulation of hot rolling is demonstrated by variation simulations of trials in a laboratory mill where the same material was used as in the basic tests. A sensitivity analysis of the rolling simulation procedure to the mode of material characterisation and the form of standard constitutive equations is thereby provided.