The potentially important ecology of subterranean predators of soil ecosystem engineers is poorly understood. This is especially true of caecilian amphibians (Gymnophiona) for which there are virtually no quantitative data. Results of the first field trials of permanent marking in caecilians are presented. A preliminary assessment is made of the efficacy of mark–recapture studies for estimating population size of Gegeneophis ramaswamii Taylor in 100 m2 of low intensity agriculture in Kerala, India. Over three sampling occasions spanning 58 days of the monsoon season, 114 individuals were captured, 104 marked and released, and 21 recaptured. Models estimate an open population of 60 individuals (95% confidence interval of 45.2 to 151.3), and a closed population of 236 (95% confidence interval of 174 to 351). A census interpretation of the raw capture data gives densities of about 0.31 to 0.48 m−2. Results suggest large movement in and out of the sampled area during the study. Despite caveats associated with these data, progress is made in identifying potential limitations and improvements in the methods used. This study highlights the paucity of knowledge of caecilian ecology, and the need for long-term studies to elucidate further ecological information and to monitor populations.