The effects of a sugar mill effluent on respiration of rice (Oryza sativa L.c.v. Mushoori) seedlings have been investigated. Each experiment consisted of two parts, the effect of various concentrations of the effluent and the time-dependent changes induced by the undiluted effluent. A marked increase in the rate of respiration was noticed upon treatment with various concentrations of the effluent. The time-dependent changes in the respiratory rate were about threefold with the 12 hr of treatment, and thereafter a rapid loss was noticed. Additionally, the respiratory quotient was studied to elucidate the nature of the metabolism of seedlings as influenced by the effluent.