Measurements　of　the　transmission　of　vibration　from　the　floor　beneath　a　seat　to　interfaces　between　the　seat　and　the　human　body　are　used　to　characterise　the　dynamic　performance　of　the　seat.　Most　studies　of　seat　transmissibility　concern　the　transmission　of　vertical　vibration　through　seat　pan　cushions,　but　fore-and-aft　vibration　at　a　seat　pan　and　backrest　can　also　cause　discomfort.　This　study　investigated　the　transmission　of　fore-and-aft　vibration　through　a　car　seat　to　surfaces　on　the　seat　pan　cushion,　the　backrest　cushion　and　the　headrest,　and　also　to　the　seat　frame　at　these　three　locations.　The　study　sought　to　understand　the　influences　of　the　seat　frame　and　the　cushion　foam　and　to　provide　data　for　dynamic　modelling　of　the　seat.　The　fore-and-aft　transmissibility　of　the　seat　was　measured　with　12　human　subjects　and　an　SAE　J826　manikin,　using　120-s　periods　of　fore-and-aft　random　vibration　(0.25-40　Hz)　at　three　magnitudes　(0.4　m/s(2)　r.m.s.,　0.8　m/s(2)　r.m.s.　and　1.2　m/s(2)　r.m.s.).　With　the　manikin,　there　were　three　resonances　(at　3.5　Hz,　12　Hz　and　20　Hz)　in　the　transmissibilities　from　the　seat　base　to　the　seat　pan　frame　and　the　seat　pan　cushion,　and　to　the　backrest　frame　and　the　backrest　cushion.　With　the　human　subjects,　the　transmissibilities　from　the　seat　base　to　all　six　locations　on　the　seat　showed　a　principal　resonance　around　4　Hz.　With　increasing　magnitude　of　the　vibration,　the　principal　resonance　frequency　in　all　the　seat　transmissibilities　decreased.　It　is　concluded　that　fore-and-aft　resonances　in　the　seat　transmissibilities,　especially　to　the　backrest,　are　likely　to　affect　vibration　discomfort.　There　are　large　differences　between　the　fore-and-aft　transmissibility　of　a　seat　with　a　manikin　and　those　with　human　subjects,　consistent　with　the　human　body　having　dynamics　very　different　from　those　of　a　rigid　mass.　Non-linearities　in　the　seat　transmissibilities　with　the　manikin　and　with　the　human　subjects　may　be　explained　by　non-linearity　in　the　biodynamics　of　the　body　and　the　responses　of　the　seat　and　the　manikin.