The level and content of different biochemical constituents were investigated over a period of one year (January–December 1982) in foot, gonad digestive gland complex and viscera of two tropical cerithiids, inhabiting two different regions of backwaters. Their seasonal indices exhibited bimodal pattern of cycling and this trend was more predominant in gonad digestive gland complex and foot. In all the body components of both species, the biochemical content was found to show considerable changes when compared to their levels. In both the cerithiids, the gonad digestive gland depicted remarkable variations with the season, followed by foot. The viscera did not show much variation when compared to other body components. The carbohydrates and glycogen of both the species showed a primary peak in March and a secondary peak in September indicating maturity of gonads. This was followed by a decline in their constituents which might be due to spawning. Lipid utilisation was also observed in both the animals next to carbohydrates and glycogen. Proteins were least utilised in the process of reproduction. Thus a carbohydrate-oriented metabolism was recorded in both the species. The results were compared with the other molluscs.