The present invention relates to a polypeptide binding to human serum albumin and comprising or consisting of an amino acid sequence selected from the group consisting of: (a) GVTLFVALYDY(X^(1))(X^(2))(X^(3))(X^(4))(X^(5)) (X^(6))D(X^(7))SFHKGEKFQIL(X^(8))(X^(9))(X^(10))(X^(11))(X^(12))G(X^(13))(X^(14))W(X^(15))(X^(16))RSLTTG(X^(17))(X^(18))G(X^(19))IPSNYVAPVDSIQ (SEQ ID NO: 1), wherein (X^(1)) is A, V, I, L, M, G, P, S, T, N, Q, C, R, H, K, D or E; (X^(2)) is R, H, K, A, V, I, L, M, G, P, S, T, N, Q or C; (X^(3)) is R, H, K, S, T, N, Q, C, F, Y, W, A, V, I, L, M, G or P; (X^(4)) is S, T, N, Q, C, A, V, I, L, M, G, P, R, H, K, F, Y, W, D or E; (X^(5)) is S, T, N, Q, C, D, E, F, Y, W, A, V, I, L, M, G, P, R, H or K; (X^(6)) is F, Y, W, A, V, I, L, M, G, P, R, H, K, S, T, N, Q or C; (X^(7)) is A, V, I, L, M, G, P, R, H or K; (X^(8)) is S, T, N, Q, C, D or E; (X^(9)) is S, T, N, Q, C, D, E, A, V, I, L, M, G, P, F, Y or W; (X^(10)) is A, V, I, L, M, G or P; (X^(11)) is F, Y, W, R, H or K; (X^(12)) is S, T, N, Q, C, F, Y or W; (X^(13)) is F, Y, W, R, H, K, S, T, N, Q, C, D, E, A, V, I, L, M, G or P; (X^(14)) is F, Y, W, A, V, I, L, M, G or P; (X^(15)) is D, E, A, V, I, L, M, G or P; (X^(16)) is A, V, I, L, M, G or P; (X^(17)) is D, E, A, V, I, L, M, G, P, R, H or K; (X^(18)) is S, T, N, Q, C, A, V, I, L, M, G or P; (X^(19)) is F, Y, W, S, T, N, Q or C; and (b) an amino acid sequence which is at least 90% identical to the amino acid sequence of (a), wherein the identity determination excludes amino acid positions (X^(1)) to (X^(19)).