Tenny-Parker Change (TPC) in chorionic villi is considered to be the consequence of uteroplacental vascular insufficiency (UPVI) characteristic of preeclamptic toxaemia (PET). Success in antenatal clinical diagnosis of UPVI claimed by some authors, using the Doppler flow technique is controversial. Other workers attribute the difficulty in reproducing these results to technical rather than biological reasons. This study evaluated the distribution of TPC in placentas from PET mothers. 2 groups of 15 each delivering at 27-3 1, and 37-40 weeks gestation were compared with 30 gestation matched controls. Tissue sampling included all gross lesions, and four specimens from apparently normal tissue. TPC, defined as small villi with prominent syncytial knots and an “expanded” surrounding maternal space was found in all cases of PET. The change, however was always patchy and invariably associated with infarction. TPC was quantified by measuring the diameter of cross sectioned terminal villi at x 10 magnification using a Quantimet 650. 10 villi were sampled from 4 fields with TPC positive and TPC negative tissue. At 27-31 weeks, mean villous diameter (in microns) was 29 2 2 (std) compared to 38 + 3 in non-TPC villi (controls 41 + 4). The TPC:non-TPC diameter ratio was 1.3. At 37-41 weeks TPC diameter was 32 + 3.9 compared to 44 + 3.5 in nonTPC villi (controls 4.08 + 0.3). The TPC:non-TPC villous diameter ratio was 1.4. The result indicates that the severe effects of chronic UPVI are patchy, and may explain the difficulty encountered with antenatal Doppler flow diagnosis.