We investigated the differences between the lavage parameters - including tumour necrosis factor-a (TNF-a) and interferon-y (IFN-y) release by lavage leukocytes - in control rats and in animals intratracheally instilled with short and long amosite and wollastonite fibres. These cytokines can play an important role in lung disease development after long-term exposure to some fibrous dusts. Short and long amosite and wollastonite fibres were intratracheally instilled in rats (1 mg/week) for ten weeks while saline was given to controls. To compare the harmful effects of these fibres, the number of leukocytes/ml of bronchoalveolar lavage (BAL), the number of alveolar macrophages (AM) per ml of BAL, AM:granulocyte (GR) ratios in lavage fluid, phagocytic activity and viability of AM, lactate dehydrogenase (LDH), acid phosphatase (AcP), and TNF-a and IFN-y release by lavage leukocytes were investigated 3 months after the first intratracheal instillation. Compared with the controls, amosite short fibres significantly decreased the numbers of AM/ml BAL, and increased their phagocytic activity and AcP release. Long amosite fibres significantly decreased the numbers of AM/ml BAL, increased the number of granulocytes depressed the phagocytic activity and viability of AM, and significantly decreased the levels of TNF-a and IFN-y in supernatants of cultured leukocytes. While wollastonite short and long fibre instillation did not significantly influence the parameters studied (except for a significantly increased number of leukocytes/ml BAL in wollastonite long fibres), amosite short and long fibres caused marked differences in these parameters, the long fibres being more effective.