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Several aminoglycoside antibiotics including neomycin, streptomycin and kanamycin have been shown to produce neuromuscular blockade in animals'-4 and in man.'-* The involvement of acetylcholine at the neuromuscular junction and at the synapse in autonomic ganglia suggests the possibility that those drugs which interfere with transmission at the neuromuscular junction may also alter transmission in ganglia. There is evidence that streptomycin, neomycin and amikacin reduce transmission in sympathetic gangliag-12 and that streptomycin and tobramycin may cause hypotension.' 3-15 Some drugs used during anaesthesia cause vasodilatation by relaxing vascular smooth muscle and by impairing transmission in sympathetic ganglia. This effect may be augmented by other, similarly acting, drugs. Therefore the effects of streptomycin, gentamycin, tobramycin and amikacin on transmission at sympathetic ganglia have been examined using the guineapig isolated hypogastric nerve-vas deferens preparation. MethodThe hypogastric nerve, hypogastric plexus and vas deferens of adult guinea-pigs (body weights 400-500 g) were dissected using a recognised method16 and mounted in 50 ml of Krebs solution at a constant temperature of 32°C.Oxygen 95% and carbon dioxide 5 % were bubbled through the Krebs solution. A parallel platinum wire electrode was used to stimulate the vas deferens transmurally and conventional unshielded bipolar platinum ring electrodes were used to stimulate the hypogastric nerve. A supramaximal rectangular wave stimulus was applied; this was 40 V for the hypogastric nerve and 100-120 V for transmural stimulation. Transmural and nerve stimuli were applied alternately for 20 s at 2 min intervals with a stimulus frequency of 20 Hz and a pulse width of 0.2 msec. Contractions of the vas deferens were sensed using an isotonic transducer (Scientific Research Instruments Ltd) and recorded with a pen recorder (Vitatron). The responses of the preparation were allowed to stabilise for 1 hr and then baseline recordings were made. Dose increments of the drug to be tested were added to the bath at 12-min intervals until complete blockade of the response to hypogastric nerve stimulation occurred. The concentration of drug in the bath was doubled when each increment was added. In this way a cumulative concentration-response association was established. The preparation was then washed thoroughly with Krebs solution and allowed to recover. The effect of each drug was measured on five guinea-pig preparations.