Lysis/resealing process for preparing erythrocytes which contain an active ingredient, the process comprising the following steps: (1) - placing a globular concentrate in suspension in an isotonic solution having a haematocrit level which is equal to or greater than 65 %, with refrigeration at from + 1 to + 8 °C, (2) - measuring the osmotic fragility based on a sample of erythrocytes from that same globular concentrate, preferably on a sample of the suspension obtained in step (1), (3) - lysis and internalisation procedure of the active ingredient, inside the same chamber, at a temperature which is constantly maintained at from + 1 to + 8 °C, comprising allowing the erythrocyte suspension having a haematocrit level which is equal to or greater than 65 % and a hypotonic lysis solution which is refrigerated at from + 1 to + 8 °C, to circulate in a dialysis cart ridge the lysis parameters being adjusted in accordance with the osmotic fragility previously measured and (4) - resealing procedure carried out in a second chamber at a temperature of from + 30 to + 40 °C by means of a hypertonic solution.
