The present invention provides illudin analogs of the general formula (I): ##STR1## where R.sub.1 is (CH.sub.2).sub.n --X--Y or H; n is 0 to 4; X is O or S or N or absent; and Y is an optionally substituted (C.sub.1 -C.sub.8)alkyl, (C.sub.6 -C.sub.10)aryl, (C.sub.6 -C.sub.10)aryl(C.sub.1 -C.sub.4)alkyl or cyclo(C.sub.3 -C.sub.6)alkyl optionally comprising one or more heteroatoms; a monosaccharide, an amino acid residue, or H when n is 2-4; R.sub.2 is absent; or R.sub.1 and R.sub.2 together comprise a 5-7 membered cyclic ring; R.sub.3 is (C.sub.1 -C.sub.4)alkyl or H; R.sub.4 is H, SCH.sub.2 CO.sub.2 (C.sub.1 -C.sub.4)alkyl, O--(C.sub.5 -C.sub.12)aryl or --S--(C.sub.5 -C.sub.12)aryl; R.sub.5 is H, OH or absent; R.sub.6 is (C.sub.1 -C.sub.4)alkyl or absent; R.sub.7 is OH or OSi((C.sub.1 -C.sub.4)alkyl).sub.3 ; or R.sub.6 and R.sub.7 together are ethylenedioxy; R.sub.8 is optionally substituted (C.sub.1 -C.sub.4)alkyl; and the bonds represented by ----- are individually present or absent. The invention further provides dimers comprising analogs of formula (I).