X-ray free electron lasers (XFELs) deliver short (<100 fs) and intense (∼10(12) 
photons) pulses of hard X-rays, making them excellent sources for time-resolved 
studies. Here we show that, despite the inherent instabilities of current (SASE 
based) XFELs, they can be used for measuring high-quality X-ray absorption data 
and we report femtosecond time-resolved X-ray absorption near-edge spectroscopy 
(XANES) measurements of a spin-crossover system, iron(II) tris(2,2'-bipyridine) 
in water. The data indicate that the low-spin to high-spin transition can be 
modeled by single-exponential kinetics convoluted with the overall time 
resolution. The resulting time constant is ∼160 fs.