Mycelial growth pellets became small and spherical on addition of Tween surfactant. Pellet particle size diminished with increased hydrophobicity (lower HLB values). Production of fructosyl-transferase from Aspergillus oryzae was enhanced by Tween 20. Filamentous pellet size depended on HLB values of the polyoxyethylene oleyl ethers. Polyoxyethylene oleyl ethers had little effect on fructosyl-transferase production.