Novel tricyclic compounds of formula (1.0) or a pharmaceutically acceptable salt or solvate thereof, wherein: one of a, b, c, and d represents N or NR, wherein R is O-, -CH3 or -(CH2)nCO2H wherein n is 1 to 3, and the remaining a, b, c and d groups represent CR or CR; or each of a, b, c and d is independently selected from CR or CR; each R and each R is independently selected from H, halo, -CR3, -OR, -COR, -SR, -S(O)tR (wherein t is 0, 1 or 2), -SCN, -N(R)2, -NRR, -NO2, -OC(O)R, -CO2R, -OCO2R, -CN, -NHC(O)R, -NHSO2R, -CONHR, -CONHCH2CH2OH, -NRCOOR, -SRC(O)OR, -SRN(R); n is 0 (zero), 1, 2, 3, 4, 5 or 6; T is -CO-; -SO-; -SO2-; or -CRR-; Z represents alkyl, aryl, aralkyl, heteroalkyl, heteroaryl, heteroarylalkyl, heterocycloalkyl, heterocycloalkylalkyl, -OR, -SR, -CRR, -NRR, formulae (i), (ii), (iii), (iv), (v) and (vi). Pharmaceutical compositions are disclosed which are inhibitors of the enzyme, farnesyl protein transferase. Also disclosed is a method of inhibiting Ras function and therefore inhibiting the abnormal growth of cells. The method comprises administering the novel tricyclic compound to a biological system. In particular, the method inhibits the abnormal growth of cells in a mammal such as a human.