The purpose of this study was to evaluate the relationship between 99mTc-MIBI (MIBI) accumulation and the response to chemotherapy. Twelve patients with small cell lung carcinoma (SCLC) underwent MIBI SPECT before chemotherapy. SPECT data were acquired 15 minutes and 2 hours after the injection of 600MBq MIBI. The early ratio (ER), delayed ratio (DR) and retention index (RI) was measured. Tumor response were classified into complete remission (CR), partial remission (PR) and no change (NC) by follow-up CT examination. The mean +/- standard deviation of ER was 3.10 +/- 0.85 (n = 4) for CR, 2.72 +/- 0.46 (n = 5) for PR and 2.43 +/- 0.95 (n = 3) for NC. DR was 3.05 +/- 1.11 for CR, 2.64 +/- 0.30 for PR and 1.90 +/- 0.82 for NC. RI was -3.0 +/- 11.69 for CR, -1.84 +/- 11.03 for PR and -18.19 +/- 38.51 for NC. CR, DR and RI were not significantly correlated with tumor response (CR, PR, NC) MIBI has the potential to predict the response to chemotherapy in SCLC.