The effect of short-chain branching (SCB) on the persistence length l(p) of polyethylene (PE) was studied using small-angle neutron scattering (SANS). In thermodynamically good solvents, l(p) can be measured directly from the scattering vector q(tr) at the crossover from good solvent mass-fractal scaling to the rodlike persistent scaling, using the unified equation described in the text. The method was used to study l(p) of both linear and branched PE in deuterated p-xylene, which is a good solvent for PE at 125 degrees C. The results indicate an increase in l(p) of the backbone chain with increasing SCB content, independently measured using Fourier transform infrared spectroscopy (FTIR). These results corroborate the behavior previously reported in Monte Carlo simulations of short-chain branched polymers. A functional relationship for l(p) in terms of the number of SCBs is proposed.