Using the analysis of HXB/BXH recombinant inbred (RI) strains, we have recently detected a suggestive association between the D6Mit9 marker and a compensatory growth of the remnant kidney after unilateral nephrectomy (P = 6 x 10(-)4). Based on conserved synteny between mice, rats, and humans, the putative quantitative trait locus (QTL) might map to a region with several positional candidate genes: for instance, the Fos oncogene was implicated as a possible candidate gene for compensatory renal growth (CRG). In the current study, we mapped the Fos gene in RI strains 27 cM apart from the position where the putative CRG regulatory QTL was detected. Despite relatively wide confidence intervals for mapping QTLs with modest effects in a small population of RI strains, this finding probably excludes the Fos as a positional candidate for CRG.