The objective of the investigations was to make innovative, improved bacterial starter cultures to be used in sourdough bread products, with the participation of strains of lactic acid bacteria (LAB) isolated from naturally fermenting sourdoughs, and to assess the usefulness of these new starter cultures for the production of bread. In the first stage, there was analyzed the micro-flora in spontaneously fermenting sourdoughs originating from traditional artisan bakeries. It was established that such sourdoughs might contain microorganisms in large numbers, which might negatively impact the bread quality. Furthermore, it was showed that approximately 40% of the analysed sourdoughs contained no lactic acid bacteria (LAB), i.e. the group of micro-organisms that, like the yeast, contributed, to the highest extent, to the taste and healthful properties of bread products. In order to improve the quality of rye and wheat-rye bread products baked in artisan bakeries, four (4) starter bacterial cultures were prepared; they all contained the LAB strains originating from an IBPRS culture collection, and isolated from naturally fermenting sourdoughs. The starter cultures produced were investigated under the micro-technical conditions; their usefulness for manufacturing wheat-rye bread products was assessed using a two-stage method of processing the sourdoughs. There were assessed properties of doughs and a quality of bread products baked using starter bacterial cultures. The best results were obtained when a starter bacterial culture containing three strains of LAB was added; the two LAB strains belonged to a Lactobacillus brevis species (one strain was from the IBPRS collection, and the second one was isolated from the naturally fermenting sourdough capable of growing at 15 °C). The third strain was a Lactobacillus fermentum from the IBPRS collection. The bread products made using this particular starter culture were characterized by the highest volume and a good quality and flavour. This culture was successfully tested in a bakery, under real production conditions. Moreover, during a one-week production cycle, it was confirmed that this starter culture was both user-friendly and useful for the bread-baking purposes. The other three starter cultures impacting the technological properties of doughs (for example the degree of souring) could also be applied to bake numerous varieties of bread products that differ in the raw material content and in their sensory qualities.