We tested the possibility that lymphocytes, sera and saliva, obtained directly from healthy human T-lymphotropic virus type 1 (HTLV-1) carriers and patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) of Iranian Mashhadi origin, as well as lymphocytes from patients with mycosis fungoides (MF) and their family relatives (MFR), may be infective. Peripheral blood mononuclear cells (PBMC), sera, PBMC cultured with phytohaemagglutinin A and phorbol myristate acetate, cell-free supernatant from these cultures, saliva cells and cell-free saliva were injected into adult WKA (n=107) and F344 (n=47) female rats. The appearance of anti-HTLV-1 antibodies in the rat sera was tested by particle agglutination assay and ELISA, and positive results were confirmed by western blot assay. Higher titers (1:1024) of anti-HTLV-1 antibodies were found in the F344 rats as compared to the WKA rats (1:256). The PA agglutination test was the most sensitive for the detection of HTLV-1 antibody. The HTLV-1 provirus was detected in both strains of rats infected with body fluids and cells from the Iranian Mashhadi Jews, in various organs (PBMC, spleen, thymus, salivary glands, spinal cord, kidney and brain) by nested PCR. However, the HTLV-1 provirus was not detected in 100% of the rats. The negative rats were only immunized and not infected. The spleen, thymus, spinal cord and salivary glands of the seropositive rats were found to be infectious and to transmit the HTLV-1 to healthy rats. F344 rats infected with PBMC cultures obtained from HTLV-1 antibody positive MF patients and their MFR who were only 20% positive showed anti-HTLV-1 antibodies, but only in 20% of rats without showing the HTLV-1 provirus; these rats were probably not infected but only immunized. This is one of the few studies on the transmission of HTLV-1 to rats by inoculation with human infectious fluids or cells from HTLV-1 infected healthy carriers (42%), HAM/TSP patients of Iranian Mashhadi origin (58%) as well as lymphocyte cultures obtained from HTLV-1 antibody positive MF and MFR of nonIranian origin.