A method for zone isolation in a subterranean producing well, the method preventing fluid flow between a formation zone, from which undesired fluids are entering and flowing in the well, and a production zone located at a distance from said formation zone, the well being provided with a pipe body, at least in a portion of the well, the method including the following steps: providing a plug over a longitudinal section of the well located between said formation zone and said production zone, the plug covering substantially the entire cross section of the well at least in a portion of the longitudinal section, so that the plug fills the inside of the pipe body and an annulus between the outside of the pipe body and a surrounding well body, wherein step also includes the following sub-steps: lowering a perforation tool into the pipe body to the longitudinal section where the plug is to be set; forming perforations in the pipe body along the longitudinal section by means of the perforation tool; by means of a washing tool which is attached to a string allowing through-flow and which is lowered to the longitudinal section, pumping a washing fluid down the string and out into the pipe body via the washing tool; by means of a directional-control means connected to the washing tool, directing the washing fluid into the annulus between the outside of the pipe body and the surrounding well body; and pumping a fluidized plugging material down the string and out into the pipe body, and thereby also into the annulus via the perforations in the pipe body. providing a plug over a longitudinal section of the well located between said formation zone and said production zone, the plug covering substantially the entire cross section of the well at least in a portion of the longitudinal section, so that the plug fills the inside of the pipe body and an annulus between the outside of the pipe body and a surrounding well body, wherein step also includes the following sub-steps: lowering a perforation tool into the pipe body to the longitudinal section where the plug is to be set; forming perforations in the pipe body along the longitudinal section by means of the perforation tool; by means of a washing tool which is attached to a string allowing through-flow and which is lowered to the longitudinal section, pumping a washing fluid down the string and out into the pipe body via the washing tool; by means of a directional-control means connected to the washing tool, directing the washing fluid into the annulus between the outside of the pipe body and the surrounding well body; and pumping a fluidized plugging material down the string and out into the pipe body, and thereby also into the annulus via the perforations in the pipe body. lowering a perforation tool into the pipe body to the longitudinal section where the plug is to be set; forming perforations in the pipe body along the longitudinal section by means of the perforation tool; by means of a washing tool which is attached to a string allowing through-flow and which is lowered to the longitudinal section, pumping a washing fluid down the string and out into the pipe body via the washing tool; by means of a directional-control means connected to the washing tool, directing the washing fluid into the annulus between the outside of the pipe body and the surrounding well body; and pumping a fluidized plugging material down the string and out into the pipe body, and thereby also into the annulus via the perforations in the pipe body.