Since 2002, the Istituto Superiore di Sanità, Rome, Italy, in cooperation with Institut Municipal d'Investigaciò Mèdica, Barcelona, Spain, has set up an external proficiency testing program (HAIRVEQ) to evaluate reliability in hair testing for drug abuse by laboratories from the Italian National Health Service. The results obtained in the last 2 rounds (2004-2005) by 26 laboratories and the evolution of the performance in hair testing for drugs of abuse by laboratories that have participated during the whole external proficiency testing program are presented. The 3 hair samples from the last exercise (2005) were also included in the proficiency test organized by the Society of Hair Testing (SoHT) and 17 international laboratories reported results. Samples analyzed in both exercises were real hair samples from drug consumers. In 2004, 2 identical samples were sent containing cocaine and opiates. One sample was a pulverized specimen and the second one was cut in short segments. In 2005, 2 samples, one containing MDMA and another containing cocaine, were included together with one blank sample. In 2004, approximately 42% of HAIRVEQ laboratories reported an erroneous qualitative result. The scatter of quantitative results was high, although no statistical differences, except for codeine, were found between results reported for the hair specimen if pulverized or reduced in short cuts. In 2005, 47 incorrect qualitative results were reported by HAIRVEQ laboratories, whereas only 5 were informed by SoHT laboratories. Concerning quantitative results, the ones from HAIRVEQ laboratories were comparable, although more dispersed, than those reported by SoHT laboratories. The scatter in quantitative results remained quite high and similar to those of the previous years; nonetheless, an improvement in the qualitative performance was observed. Considering the few number of laboratories showing a satisfying performance, guidelines have to be provided focused on method validation and qualitative and quantitative data evaluation.