Mammalian small arteries exhibit pressure-dependent myogenic behaviour characterised by an active constriction in response to an increased transmural pressure or an active dilatation in response to a decreased transmural pressure. Such responses are more apparent in distal than proximal branches. This study aimed to determine whether such responses are also a feature of amphibian arteries which are part of a low pressure circulatory system. Arteries from the common european frog (Rana temporaria) of either sex were used (body weights 12-37g). Following killing, arteries were dissected free and cannulated at either end with two fine glass micropipettes (pre-filled with Ringer solution) in the chamber of an arteriograph (Living Systems). The arteries were pressurised to 20mmHg in the absence of lumenal flow and superfused with Ringer solution at room temperature gassed with 5% CO₂ in air. Large and small mesenteric and sciatic arterial branches were used. The diameters in Ca²⁺-free Ringer at 20mmHg (μm, mean±SEM (n)) were 345±31 (9) and 179±6 (13) for mesenteric branches and 490±11 (10) and 202±18 (10) for sciatic arterial branches. Arteries were then subjected to incremental increases in transmural pressures (5-40mmHg) in the presence and then in the absence of calcium. Large arterial branches dilated with increasing transmural pressure and contractile responses were not observed subsequent to step increases in pressure. However, pressure-dependent tone was observed in large mesenteric branches in the range 15-40mmHg and in sciatic branches in the range 25-30mmHg as evidenced by narrower diameters (paired t test followed by False Discovery Rate procedure for multiple comparisons) in the presence of Ca²⁺. For example, at 30mmHg large mesenteric arterial diameters were 337±32μm and 354±32μm in the presence and absence of Ca²⁺, respectively (p<0.05); equivalent values for large sciatic branches were 507±11μm and 522±13μm (p<0.05). A clear myogenic response to a step increase or decrease in pressure was observed in small arteries (5 mesenteric and 6 sciatic vessels). At 30mmHg small mesenteric arterial diameters were 161±9μm and 183±6μm in the presence and absence of Ca²⁺, respectively (p<0.01); equivalent values for small sciatic branches were 187±21μm and 209±19μm (p<0.05). The results demonstrate that (1) amphibian arteries generate spontaneous pressure-dependent tone and (2) myogenic contractile behaviour is more apparent in smaller arterial branches. This is the first study to demonstrate myogenic contractile behaviour in arteries of non-mammalian origin.