There is evidence supporting some deviations from the standard regimen when treating pulmonary TB. Sputum culture-positive patients who are smear-negative at the start of treatment do well with only 4 months of treatment (this has not been validated for HIV-positive patients); sputum culture-negative patients do well on only 3 months of treatment (possibly because some of these patients never had TB at all). It is unwise to treat patients for only three or four months, but all TB physicians will have patients who stop their treatment early (for whatever reason), and it can be reassuring to know that sometimes retreatment is unnecessary. Elderly patients who are already taking a large number of tablets may be offered 9HR, omitting PZA which is the bulkiest part of the regimen.