This work is aimed at the development of catalytic metal complex systems for the functionalisation of methane. Methane, dioxygen, and carbon monoxide react in the presence of RhCl3-NaCl-KI system as a catalyst to form methanol, formic and acetic acids. The system activity changes on varying reaction media and increases at turning from water to aqueous organic acids, trifluoroacetic acid being the most efficient. The yield of reaction products strongly depends on mole fraction of water in the solution, carbon monoxide pressure and concentration of iodine ions. With the increase of chloride ions concentration, the yield of acetic acid passes through the maximum, the yields of methanol. formic acid and methyl trifluoroacetate decrease. The substitution of CF3COOH-H2O for CF3COOD-D2O results in a kinetic isotope effect in k(H)/k(D) similar to 1.7-2.0 for all the products formed. Hypoiodic acid and (or) hydrogen peroxide seem to be intermediate oxidants in the course of the reaction. Possible reaction mechanisms are considered.