Rice-based (Oryza sativa L.) rainfed lowlands are the major cropping system in northeast Thailand. Results of earlier research on nutrient management of rainfed lowland rice produced conflicting results with respect to inherent soil fertility, fertilizer response, and the importance of organic fertilizers, most probably as a result of highly variable soil quality and water resources. The objectives of this paper were to advance the understanding of soil fertility and fertilizer response in northeast Thailand and, thereby, provide a basic framework for improved nutrient management of rainfed lowland rice. For this purpose, we analyzed an existing data base on fertilizer trials conducted between 1995 and 1997 at eight different sites in northeast Thailand, which was previously described by Wade et al. (1999). Average annual rainfall across sites and seasons was 1300 mm, but half of all rainfed trials (12 of 23) experienced substantial water stress during the season. Average grain yield in N-omission plots was low (1.6 t ha^-1), even if compared to rainfed lowlands in neighboring Lao PDR. Nitrogen was clearly the most limiting element, whereas PK-treatments increased yields significantly in only 6 out of 78 observations. Average agronomic efficiency of applied N was good (15 kg grain kg N^-1), but highly variable between sites. Two groups of soils (i.e., sites) were separated because of their distinct differences in reaction to inorganic and organic fertilizer. Better nutrient availability consistently improved crop performance at all field water stress levels occurring at the trial sites, but the absolute response decreased with increasing water stress. We concluded, that efficient fertilizer use in rainfed rice of northeast Thailand can be achieved, but that existing uniform recommendations provide farmers with hardly useful advice. Therefore, we proposed a set of guidelines and a possible approach for improved nutrient management, which after further efforts of all stakeholders involved, could contribute to increased system productivity.