Moulting is the predominent feature of crustaceans. Cyclic cuticle deposition and resorption of calcium from old cuticle occur in relation to the crustacean moult cycle. Prolonged exposure of the prawn,Caridina rajadhari to media containing sublethal doses (0·015, 0·020, 0·025 and 0·040 ppm) of tributyltin oxide led to an apparent increase in dry weight of exuvia as well as an increase in the total quantity of calcium. The increase in weight and calcium content of exuvia was not significant in the initial two moults whereas it was significant (P<0·05) in the third moult when exposed to minimum (0·015 ppm) dose. However significant (P<0·01) rise in both exuvial weight and calcium quantity in the first two moults and highly significant (P<0·001) in the third moult exuvia were observed when exposed to maximum (0·040 ppm) dose. The observed changes in exuvia from prawns exposed to tributyltin oxide might be due to a decrease in the resorption of the old cuticle and/or due to the inhibition of chitinolytic enzymes.