Restorative effects of levamisole on general and tumor-associated cell-mediated immune responses were investigated following aniline mustard (AM) chemotherapy of BALB/c mice bearing ADJ-PC5 plasmacytoma. Total eradication of tumor following AM chemotherapy resulted in severe depression of lymphoproliferative (LP) responses which recovered after a prolonged period of 4-6 weeks. During this time, spleen cells from these treated mice were shown to be generally depressed to T- and B-cell mitogens. Levamisole, an anthelmintic drug capable of enhancing depressed immune responses in mice and in man, was employed following AM chemotherapy in an attempt to restore immunocompetency. Administration of levamisole following AM had a significant effect on the ability of mice to resist rechallenge with ADJ-PC5 tumor and in tumor cell neutralization. The enhanced resistance to tumor cell challenge appeared to be associated with a faster recovery of the general T-cell immunocompetence as demonstrated in the LP assays among the mice receiving chemotherapy followed by adjuvant therapy. Levamisole, when administered alone to tumor-bearing mice, did not appear to possess a direct antitumor effect. In addition, levamisole did not potentiate cellular immunity to higher than normal levels in nonimmunodepressed mice. These results demonstrate the efficacy of levamisole as a restorative agent of the general and tumor-associated immunocompetency in the immunodepressed host.