Pathogenicity and host-parasite relationships of Meloidogyne halpa (local population from the Plovdiv potato growing region) on potatoes were studied under field and glasshouse conditions. Potato cv. Adreta showed a typical susceptible reaction to M. halpa. In potato tubers, M. halpa induces feeding sites with hypertrophied giant cells. Infection of roots by the nematode resulted in mature galls. The relationship between initial nematode population density and growth of cv. Adreta potato seedlings was tested under glasshouse conditions. Three-week-old potato plants were infested with 0 to 64 eggs/cm3 soil. Eight weeks after inoculation, green mass (shoot weight and height) was measured, nematodes were counted in the potato roots and soil and root galling was assessed. There was a negative correlation between initial nematode densities (Pi) and growing of potato. It is estimated that a threshold limit for fresh shoot weight and height were 0.5 and 1.0 eggs/cm3 soil, respectively and the minimum possible relative values for fresh shoot weight and height were 0.65 and 0.25, respectively, at Pi=64 eggs/cm3 of soil. Root galling was proportional to the initial nematode density. Maximum nematode reproduction rate was 56.4 at a moderate initial population density (Pi=8 eggs/cm3 of soil).