Exfoliative vaginal cytology as an essential part of the gynaecological examination is a simple, non-invasive method for the determination of the phases of the oestrous cycle (anoestrus, prooestrus/oestrus, metoestrus) and is additionally applied in cases of silent heat, or suspected ovarian cysts, ovarian remnant syndrome, postpartal disturbances in the endometrial involution or Sticker sarcoma. The exfoliated cells reflect the hormonal, in particular the oestrogenic state, of the bitch. Due to the oestrogenic influence, an increase in cell layers, keratinisation and exfoliation is observed in the follicular phase during prooestrus, such that the 3-4 layered epithelium in anoestrus becomes 20-layered during oestrus. The cells change characteristically in size and nuclear morphology. In anoestrus, predominantly parabasal cells with a large nucleus and homogenous cytoplasm are found. During early prooestrus, single parabasal cells are identified among erythrocytes and intermediate cells. As this phase progresses, the percentage of large intermediate cells and nucleated superficial cells increases. The oestrus is characterised by a high cell number, initially superficial cells with pyknotic nuclei, later anucleated squamous cells that are located in cell nests. The switch to metoestrus is associated with a large number of neutrophil granulocytes and a sudden change of cytology within 24-48 hours. Vaginal cytology can be performed in any practice due to its simplicity and the limited equipment necessary (speculum, cotton wool wad, slide, staining and microscope). Because the results are rapidly available, it is a useful addition to gynaecological examination to differentiate the stage of the cycle (anoestrus, prooestrus/oestrus, metoestrus) and to diagnose infectious, inflammatory and tumorous conditions in the bitch.