We　investigated　the　association　between　the　period　of　exposure　and　changes　in　urinary　excretion　of　chromium　and　nickel　among　rotating　shift　workers　in　a　stainless-steel　plant.　The　study　participants　were　composed　of　two　groups:　the　workers　who　were　occupationally　exposed　to　metals　(＂exposed　group＂)　and　those　who　were　not　occupationally　exposed　to　metals　(＂unexposed　group＂).　The　exposed　and　unexposed　groups　consisted　of　56　and　40　male　rotating　shift　workers,　respectively.　Urine　samples　were　collected　immediately　before　and　immediately　after　the　day　shift,　evening　shift,　and　night　shift.　Urinary　chromium　and　nickel　were　measured　using　inductively　coupled　plasma　mass　spectrometry.　To　correct　for　variations　in　urine　dilution,　urinary　metal　concentrations　were　expressed　as　a　ratio　to　urinary　creatinine　concentration.　In　the　exposed　group,　post-shift　urinary　excretion　of　chromium　was　significantly　higher　than　pre-shift　excretion.　However,　although　urinary　chromium　excretion　clearly　increased　after　the　day　and　night　shift　[63%　(p　＜　.0001)　and　87%　(p　＜　.0001),　respectively],　urinary　chromium　excretion　after　the　evening　shift　was　only　slightly　higher　than　that　measured　before　the　evening　shift　(8%,　p　=　.028).　Similar　patterns　were　found　for　urinary　nickel　excretion　(p　=　.0001,　0.20,　and　0.18　for　the　day,　evening,　and　night　shifts,　respectively).　Non-uniform　urinary　excretion　of　metals　between　the　day　shift,　evening　shift,　and　night　shift　were　observed　in　the　exposed　group;　specifically,　urinary　metal　excretion　increased　only　slightly　during　the　evening　shift.　In　the　unexposed　group,　no　significant　increase　or　decrease　was　found　in　median　urinary　chromium　or　nickel　excretion　(p=　.63-0.87).　Work　shift-specific　permissible　exposure　level　would　be　necessary.