Haematological and serum biochemical measurements in male spontaneously epileptic rats (SER; double mutants homozygous for zitter and tremor genes) were compared with the values for related rat strains. Some haematological values were low in TRM rats and total leukocyte counts were high in ZI and TRM rats. TRM rats showed higher total cholesterol, phospholipid, high-density lipoprotein cholesterol and calcium values, and lower albumin value than Kyo: Wistar rats. Zitter homozygous rats including SER exhibited low total cholesterol, phospholipid and high-density lipoprotein cholesterol values. The SER showed an increase in urea nitrogen, aspartate aminotransferase and alanine aminotransferase values, and a decrease in glucose value, suggesting deterioration of the whole body with age.