the toxicological sensitivity and specificity of the micro-complement fixation test (mcf) for the detection of botulinum toxins c and d were studied in supernatants of the bacterial cultures and in livers of mice inoculated with lethal and sublethal doses. botulinum toxins c and d were produced in hemoline culture medium, titered through the determination of ld50 by the mouse test and adjusted to dilutions of 10, 1, 0.1, 0.01 and 0.001 ld50. two experimental models were used to determine the toxicological sensitivity of mcf in the supernatant of the culture medium with the dilutions described, and also in liver extracts of mice weighing 20 g and inoculated with the same dilutions. detection of the botulinum toxins was attempted in liver extracts of mice which had received lethal doses of the respective toxins, and in others which had been inoculated with sublethal doses and were sacrificed in intervals of 5 days. the results show that the toxicological sensitivity of mcf, regarding the two types of toxins at the level of 0.001 ld50, was 100% when the supernatants of the culture medium were tested; this means that the sensitivity was 100 times higher than with the mouse test. the toxicological sensitivity of mcf in the liver extracts of mice inoculated with 1 and 10 ld50 of botulinum toxins c and d was inferior, giving values of 100, 80, 89 and 72% respectively. by this test it was also possible to detect botulinum toxins type c and d in liver extracts of mice inoculated with sublethal doses, up to 15 days after the injection. the specificity of mcf was 88% and 92%, when liver extracts of healthy control mice were tested and when challenged with antitoxins c and d; and 100% when challenged with the supernatant of the culture medium. these results indicate that mcf could be of importance for research and could substitute in vivo tests.