We worked with samples of Erythromycin 250mg / 5 mL x 60mL extemporaneous preparation of suspensions of which corresponded to the laboratories Farmindustria, IQ Farma (Erytrom), LCG and samples of stable suspensions of erythromycin 250mg / 5 mL x 60mL. Cipa laboratory (Ilosone) and Genf, studied its rheological behavior and viscosity was determined by using the V1 LABOLAN rotary viscometer (Brookfield type), the analysis was conducted for 8 days under constant temperature and time. From the results obtained samples of suspensions prepared extemporaneously presented different rheological behaviors, while stable suspensions showed the same rheological behavior. Thus Farmindustria laboratories (suspensions prepared extemporaneously) and Cipa Genf (stable suspensions) showed thixotropic behavior, this being the ideal for this type of dosage form. Pharma IQ's lab presented a Newtonian behavio...