Oncologic patients are more exposed to infecto-contagious diseases (produced by bacteria, virus, fungi, and parasites) related to the own oncologic disease and chemotherapy. Neutropenia is frequent and directly related with infection risk. Approximately, 80% of patients with an absolute neutrophil count < 500 will have a febrile episode, and 20% of those with a count < 100 will have bacteremia and increased risk of infections. Patient categorization, search for organisms through conventional and biomolecular techniques, plus adequate antiinfectious treatment, directly impact on morbidity and mortality.