Efficient synthesis of large numbers of viable sphaeroplast from Saccharomyces cerevisiae has been found to be influenced by a number of factors. In this case, Trichoderma harzianum, NCIM 1185, culture filtrate has been used to prepare sphaeroplast from Saccharomyces cerevisiae, NCIM 3288. A method has been devised to isolate large number of viable sphaeroplast from the cell. Detailed analysis of various factors affecting the formation of sphaeroplasts from Saccharomyces cerevisiae has not yet been reported. This study showed critical analysis of various factors which influenced sphaeroplast formation. Most suitable conditions were: Age of the organism in slant - 1 d, cell age in liquid medium - 24 h, time of incubation of cell with 0.3% β-mercaptoethanol - 30 min, level of lytic ezyme concentration - 79.2 ml, concentration of cell (dry wt. equivalent) - 0.1262 g, time of contact with lytic enzyme - 25 min, temperature of sphaeroplast formation - 30 °C, phosphate buffer - 25 mM of pH 6.5 and KCl as osmotic stabilizer - 0.7 M. © 1992 Springer-Verlag.