Amino acid sequences are provided that are directed against/and or that can specifically bind protein F of hRSV, as well as to compounds or constructs, and in particular proteins and polypeptides, that comprise or essentially consist of one or more such amino acid sequences. The amino acid sequences, polypeptides and therapeutic compounds and compositions provided by the invention show an improved stability, less immunogenicity and/or improved affinity and/or avidity for protein F of hRSV. The invention also relates to the uses of such amino acid sequences, polypeptides, compounds or constructs for prophylactic and/or therapeutic purposes.