Twenty-eight native Bulgarian populations of Thalictrum minus complex (Ranunculaceae) show a clear correlation between the cytotype and the type of dimer isoquinoline alkaloids (2n=42 with BBI and 2n=70 with ABI alkaloids). A similar correlation is evident also in the genus Thalictrum L. There are probably different evolutionary lines: in one the biogenesis reaches to the BBI types and in the other to the ABI types.