The evolution of the size distribution in a normal and in a ferrocene (Fe(C5H5)(2))-doped laminar diffusion flame is measured with a scanning mobility particle sizer. Measurements with a low-pressure impactor and a differential mobility analyzer allow the determination of the density (rho) and the fractal-like dimension (d(f)) of particles sampled from a laminar diffusion flame. Various fuels are used and in the case of CH4, the flame is doped with ferrocene. In all cases the particle densities are low, typically below 700 kg/m(3). The data acquired from the doped flame support previous studies with ferrocene and enable us to propose a further refinement.