This report reviews formation and effects of deleterious phases in complex stainless steels and weld metals. Emphasis is on precipitation of intermetallic phases and their influences on mechanical properties and corrosion resistance. Other secondary phases such as carbides@ nitrides and secondary austenite are also discussed@ since these often coexist with intermetallic phases@ and in many cases they influence nucleation and growth rates of these@ as well as having a significant effect on properties. The influence of welding procedure and weld metal chemistry on precipitation behavior is considered. Practical detection of intermetallic phases and how to define realistic acceptance criteria is covered. The study concentrates on wrought duplex stainless steels and weld metals@ although most results can be applied to cast material. The report concludes that metallographic evaluation can provide useful information about the presence and location of intermetallic precipitates in welded joints@ but the evaluation is subject to interpretation. Evidence exists that some intermetallics can in most cases be tolerated. Acceptance of welding procedures should@ therefore@ preferably be based on direct measurement of the properties of practical concern