The formation of the ordered L10 structure from the A1 phase in nanocrystalline Fe100-xPdx (x=50–60) and Co100-xPtx (x=45–55) alloys is followed by in situ neutron powder diffraction. The A1→L10 transformation starts at about 620 and 730 K in Fe50Pd50 and Co50Pt50, respectively, and proceeds faster in the Fe–Pd alloys. In both Fe–Pd and Co–Pt, a deviation from the equiatomic composition leads to the deceleration of the ordering process. The magnetic moment of iron in the L10 FePd phase decreases with increasing Fe concentration from 3.3μB in Fe40Pd60 to 3.0μB in Fe50Pd50. In the Co–Pt alloys, the Co magnetic moment is found to be independent of the composition and degree of chemical order and is equal to 1.9μB.