In model experíments with isolated water-soluble proteins of chloroplasts the interaction of acetylcholinesterase (AChE) with ribulose-l,5-bisphosphate carboxylase (RuBPC), plastocyanin (PC), cytochrome / (cyt f) and ferredoxin (Fd) was studied. The acetylthiocholine (AThCh) hydrolysis by AChE was stimulated by other proteins by 20-200 %. Maximal effect was observed after the addition of PC. AChE itself did not affect redox capability of the electron transport carriers. The RuBPC activity was inhibited by 70 % on the AChE increase in the reaction medium. The level of inhibition was higher in the presence of the AChE inhibitors physostigmine and neostigmine, as well as the catecholamine noradrenaline. Biomediators acetylcholine (ACh), noradrenaline, adrenaline and the anticholinesterase drugs neostigmine and physostigmine slightly (by 5-20 %) inhibited the C02-fixing enzyme activity. Mutual regulation of AChE and RuBPC may exist in chloroplasts.