A total of 10 field experiments were carried out during the 1998 and 1999 growing seasons both in the north (Lleida) and the south (Granada and Jerez) of Spain. In Lleida and Granada, the experiments were conducted under both irrigated and rainfed conditions, while the Jerez trials were carried out only under rainfed conditions. Ten durum wheat genotypes were used in this study. Quality determinations consisted of 1000-kernel weight (TKW), test weight, vitreousness, ash content, protein content, pigment content and SDS sedimentation test. The influence of environment was predominant in determining the majority of quality traits, although pigment content and SDS volume were also genetically controlled. Environmental effects, studied by the mean of the climatic patterns influencing each trial, showed that total water input during grain filling appears to negatively affect grain quality by reducing test weight, grain vitreousness, and SDS volume, and by increasing ash content. High seasonal temperatures increased pigment content in the grain, but reduced TKW. From the correlations between quality parameters, an inverse and interesting relationship was found between protein content and SDS volume. Relationships between quality traits appear to be influenced to a certain extent by climatic conditions during grain filling and, depending on temperatures and water input during this phase, correlation coefficients can be either positive, negative or close to zero.