Field studies were conducted in growing seasons 2004, 2005, and 2010 to investigate the effect of different soil pH values on the alkaloid content in seeds of Lupinus angustifolius. Two-year experiments with eleven cultivars were carried out in acid soils with an average of pH=5.8 (Mecklenburg-Western Pomerania) and on calcareous soils with an average pH of 7.1 (Bavaria), respectively. In addition, in 2010, eight cultivars were grown in field experiments in soils with pH values varying between pH=5.3 and pH=6.7. In all experiments conducted on soils with a higher pH (pH=6.7 and pH=7.1), a significantly lower alkaloid content was detected in all Lupinus angustifolius cultivars than on soils with a lower pH (pH=5.3 and pH=5.8). Results clearly show that the alkaloid content is significantly influenced by the soil pH but genotypic differences regarding the reaction to different pH values in the soil were observed.