Abstract: The invention relates to a method for producing recombinant proteins by gram-negative bacteria. According to the inventive method, the products are released into the surrounding medium, thereby allowing for high expression and production rates. To this end, the gene of the recombinant protein to be produced is placed under the control of a promoter derived from a gram-positive organism, preferably from a promoter derived from the genus Bacillus that in nature does not control said gene, and a system becomes active that partially opens the outer membrane of the bacteria produced. The preferred bacteria are E. coli or Klebsiella, promoters that are not necessarily inducible from outside, especially constitutive promoters such as the &bgr;-glucanase promoter of Bacillus amyloliquefaciens (bgl promoter) and the colicin system. The protein is thereby released into the surrounding medium from where it can be easily purified.