Abstract. The investigation was performed on biological material obtained by 20 (10 male and 10 female) clinically healthy, sexually mature helmeted guinea fowl. In compliance to the norms of the Animal Ethical Committee at the Trakia University, Stara Zagora, a pair of Harderian glands was collected from each bird. Glands were individually weighed and morphometrically studied before fixation. After fixation and embedding in paraffin, permanent histological preparations were prepared from the 40 Harderian glands. Histometry of 13 main microstructural elements of the gland was performed by light microscopy and a built-in eyepiece micrometer. Data were statistically processed and presented in a table. The histometric study demonstrated that the Harderian gland of helmeted guinea fowl reared in the Republic of Bulgaria had lobules of average size 442.33 μm, outer diameter of glandular acini 49.42 μm; the outer diameter of the excretory duct of the gland was 292.40 μm, whereas the height of the lining epithelium was 21.66 μm. The results from the histometric study affirmed that by the time of guinea fowl realization on the market, the Harderian gland was a microstructurally mature and functionally active organ.