Erectile dysfunction (ED) is a common condition in men and the incidence is rising with life expectancy. There are several pharmacological agents to treat ED, but these are only partially effective. The aims are to compare the contractile activation process between normal and diseased human corporal smooth muscle and to develop an in vitro small-animal model, using guinea-pigs. Human samples were obtained with ethical approval and informed consent, from patients undergoing penile surgery. Guinea-pigs were humanely killed and the penis removed. Corporal smooth muscle strips were superfused with Tyrode’s solution (5%CO₂, 24mM NaHCO₃, pH7.4) and attached to an isometric force transducer. Inclusion of the septal membrane was avoided in guinea pigs. Contractions were elicited either by nerve-mediated, electrical field stimulation (EFS, 3s tetanic train, 0.1 ms pulses, 1-80Hz: abolished by 1 μM tetrodotoxin) or by application of phenylephrine. Carbachol and the M3-selective muscarinic antagonist 4-DAMP (4-Diphenylacetoxy-N-methyl-piperidine methiodide) were added to pre-contracted preparations. Contractions are expressed as mN/mm² and muscarinic relaxation as percentage of previously-induced contraction. Data are mean ± S.D., differences between means (p<0.05) were examined with a Mann-Whitney test. Maximum force of nerve-mediated contractions for guinea-pig tissue, Tmax, was 1.43±0.96 mN/mm² and frequency of half-maximal contraction, f1/2, was 39±2 Hz (n=15). For normal human tissue, Tmax was 0.52±0.46 mN/mm² and f1/2 42±15 Hz (n=5). For tissue from ED patients, responses to EFS were a mixture of contractions and relaxations: contractions alone (n=9), relaxation alone (n=6) and relaxations at low frequencies with contractions at higher frequencies (n=13). In the latter, relaxation Tmax was 0.10±0.2 mN/mm² (f1/2 3±2 Hz), and contraction Tmax was 0.91±1.2 mN/mm² (f1/2, 28±10Hz, p<0.05 compared to normal human tissue). Phenylephrine induced dose-dependant contractions with pEC₅₀ values: guinea-pig, 5.80±0.24 (n=10); normal human, 5.87±0.06 (n=4); human ED, 5.52±0.66 (n=17, p<0.05 compared to normal human). Carbachol relaxed both guinea-pig and human tissue, pre-contracted with 1.5 μM phenylephrine, in a dose-dependant manner, pIC₅₀=6.54±0.86 (n=8), 6.41±0.41 (n=9), respectively. In guinea-pigs, 4-DAMP (3-30 nM) decreased pIC₅₀ values. Guinea-pig is a useful animal model for human corporal smooth muscle as they display similar nerve-mediated and agonist-induced contractile responses. Tissue from ED patients exhibits increased contractile sensitivity to EFS, despite large superimposed relaxations. However, this is not due to the increased sensitivity of α-receptors as the phenylephrine pEC₅₀ was reduced in the ED group. Carbachol relaxed muscle strips pre-contracted with phenylephrine, at least in part via M3 receptors. The validation of an animal model, as applied to human tissue, will enable better characterisation of the pathophysiology of ED.