Cyclopenta[g]quinazolines of the formula (I): wherein: A is a group OR or NR0R1 wherein R0 and R1 are each independently hydrogen C1-4 alkyl, C1-4 alkenyl, C1-4 alkynyl, C1-4 hydroxyalkyl, C1-4 halogenoalkyl or C1-4 cyanoalkyl, or R0 and R1 together with the intermediate N form a five- or six-membered heterocyclic ring, p is an integer in the range 1 to 4, R2 is hydrogen C1-4 alkyl, C1-4 alkenyl, C1-4 alkynyl, C1-4 hydroxyalkyl, C2-4 halogenoalkyl or C1-4 cyanoalkyl; Ar1 is phenylene, thiophenediyl, amino, nitro, cyano, trifluoromethyl, C1-4 alkyl and C1-4 alkoxy, and R3 is a group of one of the following formulae: -A1-Ar2-A2-Y1-A5-CON(R)CH(Y4)Y5-A5-X-Ar4 and pharmaceutically acceptable salts or esters thereof are of therapeutic value particularly in the treatment of cancer.