In this paper, the results from microanalytical studies of four quenched, tempered, and stress-relieved A533 B welds are reported. Emphasis has been placed on determining the micro-distribution of copper and nickel; elements known to cause or enhance irradiation embrittlement of pressure vessel steels. Copper contents varied from 0.15 to 0.6% by weight and both high (1.6%) and low nickel (0.1%) welds were examined. Specimens have been studied using transmission electron microscope (TEM) techniques whereby chemical information can be acquired of the scale of ≥ 10 nm. In the high copper welds, copper precipitation was observed on both grain boundaries and dislocations. However, the form and extent of the precipitation has been found to be affected by the nickel level. Preliminary results from unirradiated welds on the composition of small regions (10 by 10 by 100 nm) of the ferrite, free of second-phase particles, indicate the following. First, the manganese levels in all materials and the nickel levels in the high nickel welds were in good agreement with the bulk levels. Second, in the high copper welds, the levels of copper were significantly lower than the bulk (0.5 to 0.6% by weight) and were influenced by heat treatment. The last aspect to be reported is the observation of copper sulfide particles in all the welds studied, particularly in association with large manganese silicate inclusions. The implications of this work to the irradiation embrittlement phenomenon are discussed.