A sensitive chemiluminescence method, based on the inhibitory effect of clindamycin on the chemiluminescence reaction between luminol and myoglobin in a flow-injection system, is proposed for the determination of clindamycin. The decrement of chemiluminescence intensity is linear with the logarithm of clindamycin concentration over the range from 0.1 to 70.0 ng ml-1 (r2=0.9995), with the detection limit of 0.03 ng ml-1 (3sigma). At a flow rate of 2.0 ml min-1, a complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 3.0% (n=5). The proposed procedure was applied successfully to the determination of clindamycin in capsules without any pretreatment process.