NOVELTY - New immobilized cell aggregate is new, and comprises a support and cohesive or adhesive cells. The cohesive or adhesive cells can be immobilized on the support, are capable of growth in the aggregate and a cell with lowered cell activity or a dead cell can drop out from the aggregate due to loss of its cohesive or adhesive activity.    USE - The cell aggregate is useful for the production of a desired material or for the decomposition of environmental pollutants (especially the desired product is an enzyme capable of the bioconversion of a pollutant into a non-toxic substance). The desired product is a protein, an amino acid, an enzyme, or an antibody for use in pharmaceuticals or food.    ADVANTAGE - The production of a specific material or the decomposition of pollutants is carried out efficiently, due to the ability of the cells in the aggregate to drop out from loss of cohesive or adhesive activity, therefore only living cells can remain in the immobilized cell aggregate. An immobilized cell aggregate (having the ability to produce P450), was compared to a free cell suspension (also having the ability to produce P450). The immobilized cell aggregate produced 3.16 x 10-9 mole/cell of P450, whereas, there was no detection of P450 from the free yeast, due to there being yeast with lowered cell activity and some yeast that was dead.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) the production of a desired material comprising subjecting an immobilized cell aggregate (as above) to cultivation, the cohesive or adhesive cells are capable of growth in the aggregate and can produce the desired material;    (2) a method for selecting a cohesive or adhesive cell that can attach to a support to form an immobilized cell aggregate due to a lowered cell activity or death comprising, introducing genes for cohesiveness or adhesiveness and/or genes for producing the desired material into the cell to obtain a recombinant cell, cultivating the recombinant cell with the support to form an immobilized cell aggregate, detecting and/or measuring the desired material that is produced from the immobilized cell aggregate and recovering the cohesive or adhesive cell;    (3) the preparation of an immobilized cell aggregate (as above); and    (4) an expression cassette comprising genes for cohesiveness or adhesiveness and genes for regulating the production of a desired material. The cassette is expressed to convert a non-cohesive or non-adhesive cell into a cohesive or adhesive cell, the cohesive or adhesive cell is immobilized on a support to form an immobilized cell aggregate, the cohesive or adhesive cell is capable of growth in the aggregate and a cell of lowered cell activity or a dead cell is able to drop out from the support due to loss of cohesive or adhesive activity and is expressed to produce the desired material.