Using fluorescence in situ hybridisation (FISH) the chromosomal location and relative order of six human chromosome 3 probes has been determined. The sensitivity of the technique has enabled the relative mapping of probes carrying inserts as small as 500 basepairs (bp), thus allowing the following proximal-distal probe order to be proposed: D3S30 (3p13-14), D3S4 (3p13-14), D3S2 (distal 3p14), D3S32 (3p21), D3S48E (3p21-23), and D3S11 (3p22-23). These data combined with the deletion mapping data of other researchers raise the possibility that the loss of more than one region of the short arm of chromosome 3 may be important in the development of small cell lung cancer.