An experimental study was carried out to study andcharacterize the capillary e.xtrudate swell and parisonswell behal-ior in extrusion blow molding of two commer-cial blow molding grade high density polyethylene resins.The capiIIa~ extrudate swell behavior of these resins weredetermined employing a capillary rheometer and a specialthermostatting chamber. Parison swell behavior was de-termined using an Impco Al3-R12 reciprocating screwblow molding machine in conjunction with cinematogra-phy and pinch-off. The experimental conditions underwhich capiiiaq extrudate and parison swell data can berelated are elucidated. Excellent agreement is found be-tween the area swell values determined on the basis ofcapillary and parison swell experiments.