Inhalation of dust from hard metal (HM), a mixture of tungsten carbide (WC), cobalt, and other metals, can cause interstitial alveolitis, fibrosis and asthma. Some effects of HM in the lung could occur after the metals have dissolved and penetrated the tissues. We examined in guinea-pig isolated tracheal strips whether metal salts can affect airway smooth muscle (ASM) reactivity. In unstimulated strips, the chlorides of Ni, Co, Cd evoked weak contractions (> 3 x 10^-6M; 5-15% of 120 mM KCI), while Cr2+, Cr3+, Ta5 and Zn caused relaxations (> 10^-5 M). With methacholine (MCh; 3 x 10^-7 M)-induced tone, Ni and Co caused relaxation in lower concentrations (10-7 M); the others metals caused relaxation only in high concentrations (> 1 Q-4 M). The effects of low (10^-6 M; "L") and high (3 x 10^-4 M; "H") metal concentrations on reactivity to MCh also was assessed. Co and Ta were without any effect on reactivity. Only Cd (H) affected the MCh EC50, and it decreased sensitivity. The metals affected the maximum contraction to MCh as follows: Cd, (down) (L, H); Ni, (up) (L), (down) (H); Cr2+, (down) (L, H); Cr3+, (up) (H); Zn, (up) (H). Thus, some metals (Co, Cd, Ni, Cr3+ and Zn) once dissolved might cause contraction or increase the reactivity of the ASM.