About 100 UK blood donors are being warned they may have vCJD.
The donors at risk will be notified via a letter
All gave blood to three people in 1993/4 who have since died from the human form of mad cow disease.
Precautions were brought in during 1999 when it became apparent that there was a potential for the prion disease to be transmitted through donor blood.
The Department of Health has asked the 100 donors to notify their doctors so extra precautions can be taken if they have surgery or other invasive care.
They are also being asked not to donate any more blood, tissue or organs. The department said the move was a precautionary measure.
A further 3,000 people who received blood from the donors but have not shown signs of vCJD may also be contacted.
It is not known whether the source of vCJD in the three patients who died was related to the blood that they received or BSE-infected meat that they ate.
Back in September, the government identified 17 people who received blood transfusions from people who went on to develop vCJD and sent out 6,000 letters to others informing them of the potential risk.
Since 1997 all cases of vCJD that are reported to the National CJD Surveillance Unit and diagnosed as having "probable" vCJD are passed on to the National Blood Service which searches its blood donor records.
If the patient has given blood, subsequently any stocks of that blood are immediately destroyed.
White blood cells, which it is thought may carry the greatest risk of transmitting the disease, have been removed from all blood used for transfusion since 1999.
And blood products have been prepared from plasma imported from the US since 1998.
At the end of December 2003, the total number of vCJD cases was in the UK was 145, including 139 deaths.
There is no test for the brain wasting disease so those at risk have no way of knowing whether they have vCJD.
Chief Medical Officer Sir Liam Donaldson said: "When a recipient of a blood transfusion goes on to develop vCJD, we have to consider the possibility that the infection could have been passed on through the transfusion.
"Until a reliable blood screening test becomes available, it is sensible to proceed with highly precautionary measures such as this to rule out any possibility of onward transmission of the disease."
Dr Angela Robinson from the National Blood Service said: "This notification exercise will affect in the order of 100 donors.
"If you have donated blood in the last five years and are not contacted shortly, you can be assured that you are not involved in this new safety measure and need to take no further action.
"For those people who are involved, this information may be difficult to absorb. That is why we have set up the National Blood Service helpline and are working with their doctors and other clinicians, to ensure that they have the information and support they need."
She urged the public to continue donating blood, saying that the NHS depended on this continued commitment in order to be able to save lives.