Tumour necrosis factor (TNF)α treatment of Lewis (LEW) rats neither increased the release of soluble TNF receptor I (sTNFR-I) nor induced the generation of anti-TNFα antibody. LEW rats were injectedintraperitoneally daily with 1 ml of either 105 U/ml TNFα or phosphate-buffered saline (PBS) for 3 days before Mycobacterium tuberculosis H37Ra (Mtb) immunisation, and then continued daily for a total of 10 injections. At day 9 after Mtb immunisation, blood samples were collected from these rats. The sera were then tested for sTNFR-I (A; n = 3+) and anti-TNFα antibody (B; n = 3+) by enzyme-linked immunosorbent assay (ELISA). Appropriate positive controls gave optimal results. The results of sTNFR-I are presented as mean pg/ml ± SEM, and the results of anti-TNFα antibody are presented as OD450 (mean ± SEM). *p < 0.05 and †p ≤ 0.05, when naïve sera was compared with the PBS injected-Mtb sera and TNF injected-Mtb sera, respectively.