Abstract: Methods of analyzing and controlling an electroless plating solution are described which provide for real time control of the electroless plating solution, e.g., an electroless copper bath whose main constituents are copper sulfate, complexing agent, formaldehyde, a hydroxide and a stabilizer. All necessary constituent concentrations, particularly the reducing agent concentration, are measured in situ and may be used to analyze and/or control the composition of the bath. A control cycle of less than one minute is required and hence real time control is achieved. The in situ measurements also provide quality indicia of the copper quality factors which are likewise used to control composition of the bath. Data from the in situ measurements is fed to a computer which, in turn, controls additions to the bath to maintain a bath composition which provides good quality electrolessly formed, copper plating.