Interglacial deposits resting on glacial till and overlain by fluviatile sand and gravel 2 km (1.5 miles) north-north-west of Stevenage are shown to be of Hoxnian age. The lower part of the deposit consists of calcareous silty clay formed under late-glacial and early interglacial conditions with Hippophaë shrubs and Betula woodland in a shallow water pool which contained an abundant flora and fauna. The upper part of the deposit consists of organic sediment and represents the second half of the interglacial during which coniferous trees were dominant. The fragmentary sequence, which is also found at other Hoxnian sites in Hertfordshire, is shown to result from water level changes. The recognition of these changes elsewhere in Eastern England indicates that they may be climatically controlled and thus reflect periods of alternating moister and drier conditons.