['Our purpose is to examine levels of Fas mRNA expression in blood during human corneal transplant rejection.', 'Fas mRNA expression was detected by reverse transcription-PCR in blood from normal controls, corneal recipients at the time of transplantation and during episodes of rejection.', 'Samples taken at the time of a corneal rejection episode showed Fas mRNA levels were significantly lower in these patients than either normal controls (P = 0.017) or corneal transplant recipients not undergoing graft rejection (P = 0.00052). Serial samples from five patients who suffered an episode of rejection showed that the level of Fas mRNA is reduced during the rejection episode and subsequently recovers.'] Is fas mRNA expression in blood reduced during episodes of human corneal graft rejection?