Studies on the superconductivity behaviour of pure and doped (Pb, Tl) Bi 4 Sr 3 Ca 3 Cu 4 O 16 phases are reported. Effect of oxide additives PbO, BaPbO 3 and BaBiO 3 has also been examined. Results show that an oxygen treatment at 600°C for 12 h during the final stages of the synthesis has the beneficial effect of sharpening the T c zero of the 4334 Bi-composition. Pb and T1 substitution has only a marginally beneficial effect on the T c, though it is not definitely known whether substitution is actually occurring in the system. PbO as an additive raises the T c zero to 89 K, whereas other additives do not basically affect the properties of the 4334 system. © 1989, Taylor & Francis Group, LLC. All rights reserved.