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We present the UV spectra of two quasars obtained with the Hubble Space Telescope Advanced Camera for Sur- veys (HSTACS) prism (R  100). One quasar, at redshift z ¼ 3:5, shows an absorption edge consistent either with nearlyfullyionizedheliumwithanintergalacticHeiiLyopticaldepthat3048of  304 > 3:1(90%confidence),ora Heiiiregion with edge 5.4 Mpc from the QSO. The spectrum of the second quasar, atz ¼ 3:8, has a broad absorption profile extending across the He ii emission line of the quasar consistent with a damped absorption profile from an intervening He ii system at z ' 3:7 with a column density of approximately 10 22 cm  2 . In this case, the extremely high He iicolumn density and absence of strong H iabsorption suggests that the radiation field is quite weak at 4 ryd. The combined He ii and H i signatures are consistent with photoionization by a compact (1Y100 pc) star-forming region located approximately 10 Mpc from the quasar. Subject headinggs: dark matter — intergalactic medium — quasars: individual (SDSS J1711+6052, SDSS J2346-0016) — surveys — ultraviolet: general

Intergalactic HeiiAbsorption in the Spectra of Quasars at Redshifts 3.5 and 3.8, Observed with theHSTACS Prism