Viewers of Casualty and Holby City will be able to decide the fate of patients as part of a season about the issue of organ transplants and donations.
Holby City and Casualty are set in the same hospital
The two medical dramas will combine for a special episode, with viewers able to determine the outcome of a transplant storyline by voting.
It will air later this year although a final script has not yet been written.
The BBC season - called DoNation - will raise awareness of organ donation and highlight issues surrounding it.
The season also features a five-part documentary called Life on the List, telling personal stories about organ donation.
There will also be a programme following a kidney transplant from a live donor.
A dedicated website will also offer information about the topic, explaining facts and dispelling myths.
Casualty and Holby City will join forces for their own special, where viewers will be able to vote for who will be the recipient of a donor organ.
They will be given all the facts which are available to doctors, with experts discussing what actions are open to staff.
The two series, which are set in the same fictional hospital, have previously joined up for an explosive Christmas storyline.
The BBC said the season was prompted by the statistic that although nine out of 10 people in the UK support organ donation, only two in 10 have put their names on the national register.