The aminoglycoside antibiotics possess neuromuscular blocking activity; the potency of those antibiotics tested appears to be as follows: gentamicin greater than streptomycin greater than amikacin greater than sisomicin greater than kanamycin = tobramycin greater than kanendomycin = dibekacin. The neuromuscular blockade produced by these antibiotics is not reversed by neostigmine, whereas it is reversed by calcium. Calcium not only has the ability to restore the neuromuscular transmission but also to exert protective action against the neuromuscular blocking activity of aminoglycoside antibiotics; these antibiotics are also potentially capable of interacting with non-depolarizing muscle relaxant drugs (d-tubocurarine, pancuronium) or propranolol, a beta-adrenergic receptor blocking agent. This interaction results in respiratory depression and/or prolonged apnoea. Our findings lead to the assumption that amino-glycoside antibiotics are involved in the process of acetylcholine release by nerve impulses, antagonizing calcium ions.