4-[(Heterocycloalkyl or heteroaromatic)-substituted phenyl]-2-azetidinone hypocholesterolemic agents of formula (I) or a pharmaceutically acceptable salt thereof, wherein: A is optionally substituted heterocycloalkyl, optionally substituted heteroaryl, optionally substituted benzofused heterocycloalkyl, or optionally substituted benzofused heteroaryl; Ar1 is optionally substituted aryl; Ar2 is optionally substituted aryl; Q is a bond or, with the 3-position ring carbon of the azetidinone, forms the spiro group (a); and R1 is selected from the group consisting of -(CH¿2?)q-, wherein q is 2-6, provided that when Q is a spiro ring, q can also be 0 or 1; -(CH2)e-G-(CH2)r-, wherein G is -O-, -C(O)-, phenylene, -NR?8¿- or -S(O)¿0-2?-, e is 0-5 and r is 0-5, provided that the sum of e and r is 1-6; alkenylene; and -(CH2)f-V-(CH2)g-, wherein V is cycloalkylene, f is 1-5 and g is 0-5, provided that the sum of f and g is 1-6; R?5¿ is (b), (c), (d), (e), (f), (g) or (h); R?6 and R7¿ are -CH¿2?-, -CH(alkyl)-, -C(dialkyl), -CH=CH- or -C(alkyl)=CH-; or R?5¿ together with an adjacent R?6, or R5¿ together with an adjacent R7, form a -CH=CH- or a -CH=C(alkyl)- group; a and b are independently 0-3, provided both are not zero; and when Q is a bond, R1 also can be: (i), (j) or (k); M is -O-, -S-, -S(O)- or -S(O)¿2?-; X, Y and Z are -CH2-, -CH(alkyl)- or -C(dialkyl); R?10 and R12 -OR14¿, -O(CO)R14, -O(CO)OR16 or -O(CO)NR?14R15; R11 and R13¿ are H, alkyl or aryl; or R?10 and R11¿ together are =O, or R?12 and R13¿ together are =O; d is 1-3; h is 0-4; s is 0 or 1; t is 0 or 1; m, n and p are independently 0-4; provided that at least one of s and t is 1, and the sum of m, n, p, s and t is 1-6; provided that when p is 0 and t is 1, the sum of m, s and n is 1-5; and provided that when p is 0 and s is 1, the sum of m, t and n is 1-5; v is 0 or 1; j and k are independently 1-5, provided that the sum of j, k and v is 1-5; R8 is H, alkyl, arylalkyl, -C(O)R14 or -COOR14; R9 is H, alkyl, alkoxy, -COOH, NO¿2?, -NR?14R15¿, OH or halogeno; R?14 and R15¿ are H, alkyl, aryl and arylalkyl; R16 is alkyl or optionally substituted aryl; and R19 is H, OH or alkoxy are disclosed, as well as a method of lowering serum cholesterol by administering said compounds, pharmaceutical compositions containing them, and the combination of a substituted azetidinone and a cholesterol biosynthesis inhibitor for the treatment and prevention of atherosclerosis.