A campaign is being launched to encourage more people to donate blood after it was revealed Scotland has only three days' stock of some blood groups.
The SNBTS is urging people to become blood donors
The Scottish National Blood Transfusion Service (SNBTS) said recommended guidelines state there should be at least six days supply for all groups.
Organisers of Blood Donors Week say at least 10% more donors are needed.
There are currently about 178,000 blood donors in Scotland, but numbers tend to fall away during summer months.
The issue has prompted the service to urge donors to come forward as soon as possible to avert a further stretch on resources.
Dr Moira Carter, the national donor services manager for SNBTS, said the issue was becoming more urgent.
She said: "Blood Donor Week is an opportunity to celebrate and thank Scotland's voluntary blood donors who give so willingly of their time.
"However, we currently have only three days' supply of blood in some blood groups.
"This is very worrying. Many of our donors will leave Scotland for holidays over the summer months so supplies could drop by up to 20%."
An estimated 100,000 people receive blood transfusions in Scotland each year.
The number of donors is affected by the time of year with the summer months traditionally seeing less donors coming forward.
The SNBTS is concerned that stocks could fall further as holidaymakers jet off for their summer break.
Dalkeith teenager Rebecca Smith, 16, is among those who have benefited from a blood transfusion.
She received eight units of blood and six units of fresh frozen plasma after being hit by a car in March this year.
Her extensive injuries meant she spent five weeks in Edinburgh Royal Infirmary.
She said: "The accident broke one of my legs and dislocated the other, so after my A&E care I needed two further operations.
"I'm recovering well now and looking forward to going back to school in September.
"I'd like to say thank you to all the blood donors who were there when I needed them. I'll encourage all my friends to give blood now."
Blood donors are encouraged to give blood every 12 weeks.
In particular, the SNBTS is anxious to hear from people with O negative blood which is the only blood group that can be safely given to everyone.