Аннотация:Let $\Lambda_\beta,$ $\beta>0,$ denote the Lorentz space equipped with the (quasi) norm
$$
\|f\|_{\Lambda_\beta}:=\left(\int_0^1\left(f^*(t)t\lambda\left(\frac1t\right)\right)^\beta\frac{dt}{t}\right)^{\frac1\beta}
$$
for a function $f$ on [0,1] and with $\lambda$ positive and equipped with some additional growth properties. Some estimates of this quantity and some corresponding sums of Fourier coefficients are proved for the case with a general orthonormal bounded system. Under certain circumstances even two sided estimates are obtained.