Autonomous programmable computing devices made of biological molecules hold the promise of interacting with the biological environment in future biological and medical applications. Our laboratory's long-term objective is to develop a 'Doctor in a cell': molecular-sized device that can roam the body, equipped with medical knowledge. It would diagnose a disease by analyzing the data available in its biochemical environment based on the encoded medical knowledge and treat it by releasing the appropriate drug molecule in situ. This kind of device might, in the future, be delivered to all cells in a specific tissue, organ or the whole organism, and cure or kill only those cells diagnosed with a disease. Our laboratory embarked on the attempt to design and build these molecular computing devices and lay the foundation for their future biomedical applications. Several important milestones have already been accomplished towards the realization of the Doctor in a cell vision. The subject of this proposal is a construction of autonomous biomolecular computers that could be delivered into a living cell, interact with endogenous biomolecules that are known to indicate diseases, logically analyze them, make a diagnostic decision and couple it to the production of an active biomolecule capable of influencing cell fate.