The water permeability rate of the shell wall of Bulinus tropicus (Krauss) was determined with tritiated water to be 1.74 ±1.06 μl water per 24 h. The osmotic pressure of the haemolymph increased three-fold to 300 ± 16 mOsm l⁻¹ after 60 days at 85% r.h. of the air. The [Na] of the snail tissues increased from 38 ± 9.0 mMol l⁻¹ to 68 ± 11.0 mMol l⁻¹ after 60 days at 85% r.h., but at 96% r.h. the increase changed from 40 ± 7.0 mMol l⁻¹ to 55 ± 6.5 mMol l⁻¹. The [K] of the snail tissues increased from 30 ±10.1 mMol l⁻¹ to 58 ± 11.2 mMol l⁻¹ after 60 days at 85% r.h., but at 96% r.h. the increase changed from 30 ± mMol l⁻¹ to 42 ± 10.2 mMol l⁻¹. The oxygen consumption rate (VO₂) decreased by 66% from 60.0 ±19.1μl O₂. g⁻¹ snail. h⁻¹ to 20.5 ± 16.0 μl O₂. g⁻¹ snail. h⁻¹ after 60 days at 96% and 85% r.h. In laboratory experiments without sunlight, snails were still alive after 5 months on mud. In field experiments conducted in direct sunlight on mud, snails were dead within 24 h. At r.h. of 96%, 92%, 85%, 74%, and 57% in the laboratory, the snail survival rate was respectively 40%, 40%, 42%, 22%, and 0% after 60 days. After 60 days at 96% r.h., the snail mass loss was 36%, but only 20% at r.h. of 74%.