To improve the efficiency of the glucoamylase signal peptide (GSP) of Saccharomyces diastaticus for the secretion of foreign proteins, hybrid plasmids containing one of four types of GSP mutant (m1, Pro 318 CLeu 318 ; m2, Tyr 313 CLeu 313 ; m3, Ser 39 CLeu 39 ; m4, Asn 35 CPro 35 ) were constructed and evaluated in Saccharomyces cerevisiae using Bacillus endo-1,4-L-D-glucanase (CMCase) as a reporter gene. CMCase secretion by m1, m2 and m3 GSP mutants was increased, likely resulting from a higher probability of the modified GSP to assume an K-helical structure. Especially in the case of m3, the substitution of Leu for a polar residue, Ser 39 , in the hydrophobic region resulted in approximately a twofold increase in extracellular CMCase activity. In mutant 4, which disrupts the K-helix of GSP, CMCase was less efficiently secreted. ß