The phase boundaries between the paramagnetic, superconducting, and ferromagnetically ordered states of the tetragonal pseudoternary system ${\mathrm{Gd}}_{x}{\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{4}{\mathrm{B}}_{4}$ have been determined by ac susceptibility measurements. Magnetization measurements, performed with cylindrical samples for $0\ensuremath{\le}x\ensuremath{\le}0.45$ at temperatures above 1.5 K, show clearly that macroscopic electromagnetic effects are of minor importance in this system and indicate a transition from type-II/2 to type-II/1 or type-I superconductivity at temperatures close to ${T}_{c2}$. For the critical fields we obtain from the magnetization curves a sawtoothlike ${H}_{c1}(T)$, scaling with ${T}_{c1}(x)$, whereas ${H}_{c2}(T)$ is bell shaped for $x\ensuremath{\ge}0.1$, with its maximum decreasing exponentially with $x$ for $x\ensuremath{\le}0.30$. From Arrott plots we find spontaneous magnetizations below ${T}_{m}$ and Curie-Weiss laws for the normal-state susceptibility indicating ferromagnetic Curie temperatures ${\ensuremath{\Theta}}_{c}g0$ for $xg0.1$. Analyzing the data we show that the strength of the exchange interaction between the conduction electrons and the Gd moments deduced from ${T}_{c1}(x)$ is strong enough to mediate the indirect interaction between the Gd moments as found from ${\ensuremath{\Theta}}_{c}(x)$. From specific-heat measurements carried out for $x=0.25 \mathrm{and} 0.45$ we obtain ${N}^{*}({E}_{F})=0.57$ states/(atom eV spin), in agreement with the nonmagnetic Y and Lu compounds. The details of the magnetic transitions appear to scale with the Gd concentration.