The aim of this study is to establish the effect of heating and cooling of the eyelid on the delivery of oil from the meibomian glands, as indicated by the extent of re-establishment of the reservoir of meibomian oil on the human eyelid margin, resulting from 10 conscious blinks, following pre-cleaning by a hexane swab. A standard handling sequence was followed. Step 1. Both upper and lower eyelids of both eyes of human volunteers were cleaned by a hexane swab and measured by a Meibometer to show satisfactory removal of the pre-existing oil (initial reading less than 60 instrumental units (IU)). The volunteers were then asked to blink 10 times at their normal rate. Then the eyelid was re-measured by the Meibometer. Step 2. The closed eyelids were heated for 5 min by a 250 W infrared lamp from a distance of 50 cm. The eyelid temperature was measured by an infrared thermometer, then Step 1 was repeated. Step 3. The eyelids were cooled for 5 min by an ice-pack (crushed ice in a towel). The eyelid temperature was measured, then Step 1 was repeated. Both eyes of 20 female subjects, aged 68 +/- 3 S.E.M. (range 52-84) years were examined. The mean instrumental reading (IU +/- S.E.M.) after 10 blinks at 33.4 +/- 0.1 degrees C was 154 +/- 12. On increasing the eyelid surface temperature by 4.9 +/- 0.3 degrees C we obtained an increase of 49 +/- 9 IU. On decreasing it by 7.6 +/- 0.4 degrees C we obtained a decrease of 46 +/- 9 IU. We conclude that temperature significantly influences the delivery of the meibomian gland secretion. Our results are in agreement with the 10-blink recovery value of 191 +/- 9.3 IU previously reported. They also agree with the reported benefit of warm compresses to improve delivery from dysfunctional glands. The most likely explanation for our findings is a change in the viscosity of the meibomian oil.