The absorption of H2O and D2O was studied in seeds with different reserve food materials represented by barley and rice (starch), linseed and mustard (fat) and mung, and kidney beans (protein). Respiration rate and respiratory quotient during absorption were also measured. The results indicate that the water absorption profiles of the starchy and fatty seeds are essentially similar but differ from that of The proteinaceous type. Initial hydration is relatively incomplete in D2O in all The seeds to varying degrees the latter being maximum in The proteinaceous and minimum in The starchy seeds. The respiration rate is lower in D2O while The R.Q. values are higher for The first hour but lower later on. The results, in part, help explain The varying effects of D2O on The germination of different types of seeds. These studies also support The earlier reported preference (Cope et al. 1965) by the higher plant systems for protium.