With around 24 hours of in game playtime (around 18-19 of those being on a single character) I haven't gotten any blood to regenerate. I've kept my belly full and used the wiki as a guide to get a rough estimate on my "energy" and "water" from food. The health regeneration was supposed to kick in but it didn't. I think most of the people explaining how to regenerate blood are just regurgitating what Rocket has stated without actually getting it to work themselves (assumption; I could be wrong). Currently the only ways to heal yourself seem to be: 1. Saline IV (loot found in hospitals) 2. Harvest blood from survivors at gunpoint (Since you lose blood in a blood donation this seems the only way to get a willing donor) 3. Suicide and respawn (Out of the question if you enjoy any kind of immersion what-so-ever) From experience I've found it's best to save Saline until you're pretty low on blood so as not to waste a drop. Also don't be conservative with your ammo. Its easier to find bullets than Saline so shooting a zombie is better than fighting it melee since their movement is still rather jumpy and they can get random hits in.