To provide the building blocks for making synthetic antibody fragments we have used the polymerase chain reaction (PCR) to clone human variable (V) gene segments of lambda light chains. The PCR primers were based on the sequences of known human V lambda segments, and were used to isolate 14 new V lambda segments (including 4 pseudogenes) from a single individual. We have compiled a sequence directory from this data and other sources to include all known human V lambda segments with open reading frames and we have identified a new V lambda family (V lambda IX). Almost all of the segments (22/24) have different sequences in the complementarity-determining regions, setting a lower limit to the structural diversity of the antigen binding sites encoded by human V lambda genes in the human population.