Thermal gradients were measured from the cornea to the posterior pole in the eyes of 11 chicks, six of which had the lids of one eye sutured three weeks previously. A comparison was made between eyes that were chronically closed by lid-suture (while still sutured shut) and two types of control eyes: (a) treated controls, which were the non-sutured, contralateral eyes of the lid-sutured chicks and (b) untreated controls, which were the eyes of a different group of chicks in which neither eye had been sutured. The results indicated that transient closing of the eyes of normal, untreated chicks (untreated controls) elevated the ocular temperature by about 1.5°C at the cornea; the extent of thermal elevation diminished as the thermoprobe was advanced towards the posterior pole. In contrast, when the transiently closed eyes in untreated control chicks were compared with the chronically closed eyes of the lid-sutured chicks, the lid-sutured eyes were cooler by 2°-2.5°. When the sutured lids were opened, however, the eyes were isothermal with the untreated control eyes. Moreover, the eyes of lid-sutured chicks were isothermal with their contralateral, non-sutured, control eyes (treated control), whether in the opened or closed state. A comparison of the untreated control eyes and the treated control eyes revealed no differences (except at the cornea) when the eyes were opened; but when the eyes were closed, the treated control eyes were 2°-3°cooler than the untreated control eyes. These results indicate that chronic lid suture produces very different effects on the thermal properties of the eye than does transient lid closure. Chronic lid closure results in a reduction of ocular temperature when the eyes are closed, which may be a consequence of the sutured eye's reduced need for vascular thermoregulation by the choriocapillaris circulation. The differences between lid suturing, which reduces ocular temperature, and the application of goggles, which elevates ocular temperature, are discussed.