Serum thyroxine(T4), effective thyroxine index(ETI) and thyroid stimulating hormone(TSH) were measured in 60 albino rats following laminectomy and cord injury produced by weight drop method. Thyroid hormones were measured at one and 100 minutes and, at 1, 3 and 7 days after injury by radioimmunoassay method. At 1 and 100 minutes, T4 was significantly reduced in both laminectomy and cord injured groups. TSH at 1 and 100 minutes were also elevated significantly. Gradual normalization of T4 and TSH showed at 7 days. It appeared likely that the opimal time to the administration of exogenous thyroid hormone would be before the 7th day of cord injury.