The present invention relates to novel muteins derived from human lipocalin 2 (hNGAL) and related proteins that bind a given non-natural ligand with detectable affinity. The invention also related to corresponding nucleic acid molecules encoding such a mutein and to a method for their generation. The invention further relates to a method for producing such a mutein. Furthermore, the invention is directed to a pharmaceutical composition comprising such a lipocalin mutein as well as to various uses of the mutein.