Necropsies on 43 horses, 35 donkeys and two mules slaughtered in Ankara, Turkey, revealed that 12 (15%) of the equines harboured adult Setaria equina. When blood samples were checked for microfilariae, using Knott's method and a combination of membrane filtration followed by histochemical staining for acid phosphatase (AP), only three (4%) of the animals were found to be microfilaraemic. When stained for AP, the S. equina microfilariae exhibited diffuse red staining over the entire body, including the sheath, with brighter staining around the anal and excretory pores. Application of Knott's method revealed only two of the three microfilaraemias detected using the combination of filtration and AP staining. The combination may represent a useful technique for the detection of equine microfilaraemia.