THREE strains of yeast fungi namely Saccharomyces cerevisiae (Baker's yeast), Rhodotorula glutinis and Geotrichum candidum were tested for their potency in biosynthesis of AgNPs by direct exposure to silver nitrate solution. Absorption UV-Visible light spectroscopy is used to follow up with the reaction process. Transmission electron spectroscopy (TEM) is used to produce detailed information on the progress of reduction of silver nitrate (formation of silver nanoparticles) on the nanosecond timescale. Our measurements indicate that extracellular biosynthesis of silver nanoparticles AgNPs by different yeast strains produce AgNPs with the diameters in the range of 2.5-20 nm. The three yeast strains are environmentally friendly microorganisms, and they are known for their formation of extracellular enzyme and metabolites in very large amounts, which could be utilized in AgNPs synthesis. The present work is undertaken with a view to accomplish controlled size and shape of AgNPs by making use of the yeasts to manipulate key parameters which control growth and other cellular activities