Lysis/resealing process for preparing erythrocytes which contain an activeingredient (e.g. aspariginase or inositol hexaphosphate), the processcornprising the following steps: (1) placing a globular concentrate insuspension in an isotonic solution having a haematocrit level which is equalto or greater than 65 %, with refrigeration at from + 1 to + 8 ~C, (2)measuring the osmotic fragility based on a sample of erythrocytes from thatsame globular concentrate, preferably on a sample of the suspension obtainedin step (1), (3) lysis and internalisation procedure of the active ingredient,inside the same chamber, at a temperature which is constantly maintained atfrom + 1 to + 8 ~C, comprising allowing the erythrocyte suspension having ahaematocrit level which -is equal to or greater than 65% and a hypotonic lysissolution which is refrigerated at from + 1 to + 8 ~C to circulate in adialysis cartridge the lysis parameters being adjusted in accordance withthe osmotic fragility previously measured and (4) resealing procedure carriedout in a second chamber at a temperature of from + 30 to + 40 ~C by means of ahypertonic solution.
