In Republic of Karelia a significant reduction in potato productivity and loss in yield quality are connected with crop infestation by fungal, viral diseases and globoderosis. Potato plants are often infected by two or more pathogenic organisms, and in these cases phytopathocomplexes are formed. Aim of study was to investigate potato plant responses to infection by pathogens and combined with potato cyst-forming nematode (PCN) infestation. The effect of rhizoctoniosis (agent of a disease – fungus Rhizoctonia solani Kuhn.), virosis (X- and Y-viruses), globoderosis (PCN Globodera rostochiensis Woll.) on potato (cv. Nevsky) growth and biomass formation was studied. It was established that all infestation combinations, especially with PCN, stimulated plant growth at early stages of ontogenesis and inhibited at the late stage of plant development. Morphometric parameters and weight of above- and underground parts of potato plants were lower as compared with control plants. Combinations “fungus+nematode” and “fungus+nematode+X virus” were the most unfavourable for plants.