Exon 3 and 0.6 kb of downstream intronic sequences containing the exon/intron boundary was replaced with a neomycin resistance gene via homologous recombination. Absence of mRNA and protein expression in homozygous mutant animals was confirmed by Northern blot analysis of brain and liver tissue using a cDNA probe to rat Igfbp2 and by Western blot analysis of serum proteins. (J:64338)