Standard neutron fields of isotope neutron sources, established in the Institute of Atomic Energy, Poland, have been examined for nearly 20 y. The neutron dose equivalent and gamma dose rates were measured, applying various techniques. The neutron emission of standard neutron sources of 241Am-Be and 252Cf has been originally determined in primary standard laboratory, then checked, making use of transfer instrument calibrated in primary laboratory. The growth of neutron emission of 239Pu-Be source, used for routine calibrations, has been demonstrated. The total uncertainty of determined parameters has been discussed. The periodically repeated checks of neutron fields of standard sources with the use of transfer instrument, calibrated in primary laboratory, should provide the traceability to primary laboratory and the fields could be officially recognised.