Bronchoalveolar lavage (BAL) a technique which is not very invasive and which permits investigations of deep lung reactions from various causes, has been demonstrated to be also useful in the diagnosis of lung disorders from hard metals (HM) and/or cobalt, thus overcoming, in most cases, a need for open lung biopsies. Cases with HM interstitial disease show at BAL the signs of a high-intensity alveolitis, characterized by increased total cells with bizarre multinucleated giant cells and increased inflammatory cells. These findings correspond well to the histological pattern of desquamative giant cell interstitial pneumonitis. The persistence of alveolitis and especially high numbers of eosinophils at following BALs, despite cessation of exposure and steroid treatment, has an ominous prognostic significance. The few reported cases of cobalt asthma studied by BAL present either normal findings or increased T lymphocytes with inverted helper/suppressor ratio. This last finding has also been described in some asymptomatic exposed subjects, which indicates a subclinical (or preclinical?) lung reaction. Determination by neutron activation analysis of trace metals (cobalt, tungsten, tantalum) in BAL and other biological specimens may be important in documenting recent or past exposures, but is not discriminant for diagnosis, since no relationship has been found between levels of any metal and the occurrence of the disease.