In prior studies, we and others have documented a significant reduction by surface chemistry modification in the biological activity of quartz. We further documented that aluminium lactate inhalation one month after quartz exposure significantly suppressed the silica-induced alveolitis, reduced the pathological process and decreased the retention of quartz in the lung tissue. In the present study, we evaluated the efficacy of aluminium inhalation in altering the silicosis process after disease was recognized by standard chest radiography. Twenty-four sheep were enrolled in the study. The 14 silica exposed sheep had an abnormal chest radiograph of the ILO category 1 or above after 3 years of 100 mg Minusil-5 in 100-ml saline intratracheal injections. Ten control sheep were exposed to saline intratracheal injections. All sheep were evaluated at 3-month intervals by chest radiography, lung function and lung lavage. At month 36 of the study, all 14 sheep had an abnormal chest radiograph while the radiographs of controls remained normal. The sheep with silicosis had significantly reduced lung functions and increased cellularity, phospholipids and hyaluronan. These changes persisted during the next 12 months without exposure or treatment. At month 48 and at monthly intervals after, for 12 months, aerosol inhalations were carried out with saline alone for control and seven silicotic sheep and with 100 mg of aluminium lactate in 10 ml saline generated with a Bird Mark 8 pressure ventilator for the other seven silicotic sheep. All sheep were evaluated at 3-month intervals by chest radiography, lung function and lung lavage.(ABSTRACT TRUNCATED AT 250 WORDS)