beta -Galactosidase and streptokinase expression was tested under the control of the T7 promoter in batch and fed-batch cultures. An Escherichia coli host GJ1158, which contained the T7 RNA polymerase gene under the osmo-responsive proUp promoter, was used for expression studies. beta -Galactosidase expression was enhanced from 26 mg l(-1) to 127 mg l(-1) in batch culture when a combination of sucrose and sorbitol was used instead of salt as an inducer. Similarly in fed-batch cultures 140 mg streptokinase l(-1) was formed with sucrose and sorbitol induction which was higher than that achieved with IPTG induced cultures.