This study was undertaken to investigate effects of gossypol poisoning in broiler chickens which were fed with cottonseed and cottonseed meal. Poisoning related findings were compared between the two groups. For this purpose, a total of 10 day old 117 Ross PM-3 broiler chickens without sex determination, were divided into three main groups: two trial groups (n=104) and one control group (n=13). Each trial group was further subdivided in four subgroups each containing 13 chickens. In the group I (trial group I), cottonseed was added to standard diets as: 5 % (subgroup 1), 10 % (subgroup 2), 15 % (subgroup 3) and 20 % (subgroup 4). In the group II (trial group II), cottonseed meal was added to standard diets as: 10 % (subgroup 1), 20 % (subgroup 2), 30 % (subgroup 3) and 40 % (subgroup 4). Feeding experiments were carried out for 8 weeks. In the present study, no significant clinical and pathological findings were observed in the subgroups 1, 2 and 3 of the trial group II chickens. Such findings in the subgroup 4 were mild or difficult to distinguish. Both clinical and pathological toxic effects were seen in the trial group I. Clinically, starting from the third week of the experiments, a significant decrease in body weight, weakness, dilatation of the crop, fall down in the chest position 4-9 hours before death and terminal convulsions following lying on a side were observed. Mortality rate was recorded as 26.15 %. Macroscopically, yellow coloured fluid in the pericardium and abdomen; congestion and oedema in the lung; an accumulation of frothy fluid in the caudal part of the trachea and cross sections of the lung; bilateral dilatation of the ventricles in the heart; enlargement in the oesophagus and crop; diffuse focal ulcers on the mucosa of the ventriculus, crop and oesophagus; severe congestion and focal necrosis in the liver were noted as the main findings. Microscopic lesions related to macroscopic ones were characterized with congestive heart failure and its complications. Toxicologically, free gossypol levels were determined in the heart (24-248 ppm) and liver (74-316 ppm) tissues sampled from all subgroups of the trial group I. In the trial group II, no gossypol was found in the subgroups 1, 2 and 3. However, there were low levels of free gossypol (12 ppm) only in the liver samples of the subgroup 4.