To examine the photodynamic therapy (PDT) effect on adipocytes, we investigated whether PDT using DH-I-180-3, a new synthetic lipophilic photosensitizer, induced cell death of both undifferentiated and differentiated 3T3-L1. 3T3-L1 pre-adipocytes were differentiated into adipocytes in the culture medium containing pantothenate, insulin, dexamethasone, isobutylmethyixanthine, and troglitazonc. PDT was applied to both undifferentiated and differentiated 3T3-L1. Photosensitizer uptake in fat cells was determined by measuring its mean fluorescence intensity. DH-I-180-3 mediated effectively PDT-induced cell death of both pre-adipocytes and adipocytes. And the photosensitizer was accumulated more rapidly in 3T3-L1 adipocytes, compared with other cancer cell lines. These results demonstrate that PDT is a potent cell death inducer in pre-adipocytes and adipocytes. Thus, PDT with DH-I-180-3 may be applied for a new therapeutic modality for obesity treatment. (c) 2005 Elsevier Inc. All rights reserved.