Anesthesia is used in theraphosid spiders to facilitate medical procedures (e.g., physical examination, sample collection, surgery); however, most information on this subject is anecdotal. This study was conducted to systematically determine the anesthetic parameters of wild-caught, subadult goliath birdeater spiders (Theraphosa blondi) (n  =  11) and Chilean rose spiders (Grammostola rosea) (n  =  12). Each spider was placed in a 3-L gas anesthetic chamber and subjected to an induction of 5% isoflurane at a rate of 1 L/min oxygen. Anesthetic depth was monitored by evaluating the righting reflex every 5 min. Animals were recovered in 100% oxygen. Induction, recovery, and overall anesthetic times were determined. After an 8-wk washout period, the procedure was repeated. For both species, median induction time was 10 min. Median recovery time was 30 min for T. blondi and 12.5 min for G. rosea.