The gold method was further developed for fluorescent microscopy. Gold granules (12 nm in size) were labelled with rhodamine conjugates of Concanavalin A and avidin. The fluorescent markers were used to mark cell wall mannan on the yeast Saccharomyces cerevisiae either by the one-step, or by the two-step method via a biotinyl derivative of ConA. By fluorescence or transmission electron microscopy, the two-step method was found to achieve a higher density of marking.