The result of post mortem and examinations on 1276 chickens in Thai Nguyen and Bac Giang province showed that: 617 chickens were infected by Heterakis gallinarum, the infections rates of Heterakis gallinarum was 48,35 percent
244 chickens were infected by Histomonas meleagridis, the infections rates of Histomonas meleagridis was 48,35 percent. There was a correlation between the infections rates of blackhead disease and that of Heterakis gallinarum. Which locations had higher proportion of chickens infected by Heterakis gallinarum also had higher infections rates of blackhead disease and in contrast. Analyzing collected data by using version 14.0 of Minitab software demonstrated that there was a strong correlation between Heterakis gallinarum and blackhead disease with R = 0,947. The floor inside the pen, the ground around the house, and grazing area were contaminated by pinworm eggs at the rates of 49.84 percent, 40.32 percent, and 26.27 percent respectively.