An investigation has been made of the solution used for the chemical bath deposition (CBD) of In(OH,O)(x)S-y thin films. In order to identify intermediate steps in the deposition process, the sulfur source was at first omitted. Optical light absorption measurements and transmission electron microscopy have shown that mainly free indium(III), polynuclear indium hydroxo-complexes, and already formed In(OH)(3) colloids are involved in the nucleation and growth of the layers. Precipitation and coherent film growth could only be observed once the sulfur source, thioacetamide, was added to the solution, leading to the formation of In(OH,O)(x)S-y. The composition of these CBD layers was analyzed using elastic recoil detection analysis. This allowed the observation of the hydrogen content and thus enabled a possibility to judge the incorporation of hydroxide into the layer. Finally, a tentative reaction scheme for the formation of In(OH,O)(x)S-y is presented.