The ideal cancer treatment modality should not only cause tumor regression and eradication but also induce a systemic antitumor immunity, which is essential for control of metastatic tumors and for long-term tumor resistance. Laser immunotherapy using a laser, a laser-absorbing dye, and an immunoadjuvant has induced such long-term immunity in treatment of a mammary metastatic tumor. The successfully treated rats established total resistance to multiple subsequent tumor challenges. To further study the mechanisms of the antitumor immunity induced by this novel treatment modality, passive adoptive transfer was performed using splenocytes as immune cells. The spleen cells that were harvested from successfully treated tumor-bearing rats provided 100% immunity in the naive recipients. The passively protected first cohort rats were immune to tumor challenge with an increased tumor dose; their splenocytes also prevented the establishment of tumor in the second cohort of naive recipient rats. This immunity transfer was accomplished without the usually required T-cell suppression in recipients.