One of the most important but infrequent complications of discectomy is discitis. On the other hand, major surgical operations usually induce a transient increase in erythrocyte sedimentation rate (ESR). So in order to use ESR as a screening tool in diagnosis of deep infection after discectomy such as discitis, we must measure it in patients after discectomy but without any complication. This is a prospective study on 50 patients after discectomy. Inclusion and exclusion criteria consists of: 1- Patients must have preoperative ESR within normal range, 2- No clinical or laboratory sign of systemic illness preop., 3- No fever or other signs of infections must be found in patients postoperatively.We measured ESR before operation and in days 1, 3, 5, 7, 14, 21, 28 and 35 after operation. After discectomy in most patients ESR rose rapidly and reached its maximum by the third day after operation. As a whole, greater values of ESR were seen in patients whose operation involved more disc spaces. In most patients with one disc ESR reached its normal range 2 weeks after operation, but in patients whose operations involved more disc spaces, ESR reached its normal range by the fifth weeks. If after 2 weeks ESR does n't reach its normal range, in patients whose discectomy involves only one level or after 5 weeks in patients whose discectomy involves more than on level, we must suspect discitis if other signs of infection do exist. If the diagnosis of discitis is delayed, serious complications may occur.