The International Atomic Energy Agency (IAEA) coordinates the work of a world-wide network of analytical laboratories, the Analytical Laboratories for the Measurement of Environmental Radioactivity (ALMERA) network. A proficiency test for ALMERA members was organized in 2006 based on the determination of gamma-emitting radionuclides ((54)Mn, (60)Co, (65)Zn, (109)Cd, (134)Cs, (137)Cs, (241)Am and (210)Pb) in three matrices: water, soil and grass. This paper presents the methodology applied in this proficiency test and discusses the results of the analytical performance evaluation for 38 participating laboratories. The paper also addresses some technical root causes, which could explain low performances in the determination of (109)Cd and (210)Pb.