The efficacy of aqueous alkaline solutions to purify wastewater sludges destined for agricultural land application was evaluated. Some fecal bacteria were tested as sanitary-quality indices, these included fecal streptococci, which were found to be more resistant than coli-forms. Hygienization within 10 days was obtained with ammonium hydrate at a dose that brought the pH of the sludge to about 10. Such a treatment was effective above 10 degrees C. The total-bacteria number dropped only slightly, so that the sludge retained its potential biological activity. The efficacy of the treatment with NH4OH was better than that observed with KOH.