Increasing efficiency of detection of low MW restriction fragments. Using Klenow DNA polymerase and a probe with a sub-family specific 3' end and 10x G residues at the 5' end, the efficiency of the labelling reaction could be increased ten fold. Degenerate sub-family centred PCR was performed using the Kir 2.0 subclones as template, labelled as described in Materials and Methods, and digested with Hinf I. Low molecular weight fragment (<50 bp) end-labelling was significantly improved. Generated end-labelled fragments from Kir 2.1, 2.2, and 2.3 were in agreement with predicted sizes of 147, 400, and 55 bps respectively. Gel images were scanned and processed using Adobe Photoshop Version 5.5.