The tripeptide sequence asparagines?glycine?arginine (NGR) specifically recognizes aminopeptidase N (APN or CD13) receptors highly expressed on tumor cells and vasculature. Thus, NGR peptides can precisely deliver therapeutic and diagnostic compounds to CD13 expressing cancer sites. In this regard, 2 NGR peptide ligands, HYNIC?c(NGR) and HYNIC?PEG_2?c(NGR), were synthesized, radiolabeled with ^99mTc, and evaluated in CD13 ? positive human fibrosarcoma HT?1080 tumor xenografts. The radiotracers, ^99mTc?HYNIC?c(NGR) and ^99mTc?HYNIC?PEG₂?c(NGR), could be prepared in approximately 95% radiochemical purity and exhibited excellent in vitro and in vivo stability. The radiotracers were hydrophilic in nature with log P values being − 2.33 ± 0.05 and − 2.61 ± 0.08. The uptake of 2 radiotracers ^99mTc?HYNIC?c(NGR) and ^99mTc?HYNIC?PEG2?c(NGR) was similar in nude mice bearing human fibrosarcoma HT?1080 tumor xenografts, which was significantly reduced (P< .05) during blocking studies. The 2 radiotracers being hydrophilic cleared rapidly from blood, liver, and intestine and were excreted through renal pathway. The pharmacokinetics of ^99mTc?labeled HYNIC peptide could not be modulated through introduction of PEG 2 unit, thus posing a challenge for studies with other linkers towards enhanced tumor uptake and retention.