The beta-carbolines harmane, norharmane, tetrahydronorharmane, harmine, harmaline and harmol were administered to sheep to assess their effects on upper motor neurone function. Harmane at a dose rate of 54 mg/kg induced hypomotility, head tremors, pelvic limb paresis, hypermetria and a wide based stance. A range of similar effects were observed with norharmane at the same dose rate. Tetrahydronorharmane at a dose rate of 54 mg/kg induced hypermotility followed by hypomotility, asymmetrical pelvic limb paresis, hypermetria, a wide based stance, and stereotyped eating behaviour. Harmine and harmaline at 6 mg/kg induced mild head and body tremors, and at 18 mg/kg induced hypomotility, intense head and body tremors, pelvic limb paresis, crossing over of limbs, neck extension and head swaying. Harmol was not effective at 54 mg/kg by either the subcutaneous or intraperitoneal routes, but at an intravenous dose of 27 mg/kg it induced hypermotility followed by hypomotility, body tremors, limb paresis, muscle asynergy, a wide based stance and jumping behaviour. Harmane, tetrahydronorharmane, harmaline and harmol were convulsive in some sheep at high dose rates.