AbstractNine crude drugs containing tannins were selected in order to examine their actions on rats with renal failure. The levels of urea nitrogen, creatinine (Cr), methylguanidine (MG) and guanidinosuccinic acid (GSA) were decreased markedly and significantly in rats given Ephedrae Herba. Chebulae Fructus and Geranii Herba produced the same effect on uraemic toxins as that of Ephedrae Herba. MG was significantly decreased by all tannin‐containing crude drugs. However, there were no particular changes in these parameters after administration of non‐tannin‐containing crude drugs. The levels of urea nitrogen, Cr, MG and GSA showed a tendency to be increased in rats given Rehmanniae Radix, Coptidis Rhizoma, Scutellariae Radix and Alismatis Rhizoma, but MG was decreased significantly in rats given Bupleuri Radix. Non‐tannin compounds also produced no significant decreases in the levels of uraemic