Reptile euthanasia techniques are poorly described. This nonblinded randomized study compared pentobarbital, lidocaine, and potassium chloride (KCl) for leopard gecko (Eublepharis macularius) euthanasia at 20°C (68°F) and evaluated for postmortem artifacts. Fifty-three clinically healthy adult leopard gecko were scheduled for euthanasia due to Cryptosporidium varanii exposure. Based on pilot-study results, geckos randomly received one of six treatments: intracoelomic (ICo) pentobarbital 400 mg/kg (ICo-P4, n = 9) or 800 mg/kg (ICo-P8, n = 9), intramuscular (IM) alfaxalone 20 mg/kg followed by intracardiac (ICa) pentobarbital 800 mg/kg (ICa-P, n = 9), KCl 10 mEq/kg (ICa-K, n = 9), or lidocaine 100 mg/kg (ICa-L, n = 9) or IM alfaxalone 20mg/kg (IM-A, n = 8, control). Serial Doppler heart rate assessments were performed until cardiac arrest, 30 min (ICa groups), or 60 min (ICo groups) posttreatment. Cardiac arrest occurred in 7/9, 9/9, 9/9, 8/9, and 8/9 geckos in ICo-P4, ICo-P8, ICa-P, ICa-K, and ICa-L, respectively, with median (range) times of 35 (25–45), 30 (15–60), 0 (0–6.33), 0 (0–0.05), and 0 (0–0.03) min. Side effects were noted in a subset of ICo-P (arched posture) and ICa-K (muscle spasms) geckos. Six geckos in ICa-L had Doppler sound resumption several hours following cessation, with three displaying spontaneous movement. All geckos in IM-A recovered. Intracardiac pentobarbital following IM alfaxalone caused rapid, permanent loss of heartbeat in all tested geckos. Intracoelomic pentobarbital was also effective, but had a prolonged time to cardiac arrest. Intracardiac lidocaine is not recommended for leopard gecko euthanasia.