Plasmid Slots allow the player to equip active Plasmids. Plasmid slot upgrades allow the player to carry one more Plasmid per slot purchased.
Plasmid Slots are purchased at Gatherer's Garden machines throughout Rapture for 100 ADAM each. The price does not change during the game. The player can have a maximum of six Plasmid Slots, meaning the player can purchase up to four slots.
Plasmid Slots return to the sequel as a purchasable upgrade. Although the price has been decreased to 40 ADAM, the price increases by 10 ADAM with each successive purchase; however, the last two Plasmid Slot upgrades cost 70 and do not increase in cost. The player can also purchase up to five Plasmid Slots this time which, combined with the three Plasmid slots available from the start, brings the total to a maximum of eight slots. If the player has not purchased all available Plasmid Slots by the time they receive the Summon Eleanor plasmid, a slot will automatically open up so the player can equip it.
In Minerva's Den, the fourth Plasmid Slot is already available to the player, as Subject Sigma wields Telekinesis from the start. As a result, the cost of the Plasmid Slots start at 50 ADAM and increase with 10 ADAM with each successive purchase; just as the main game, the last two Plasmid Slot upgrades cost 70 and do not increase in cost. The player can purchase up to four Plasmid Slots this time which, combined with the four Plasmid slots available from the start, brings the total to a maximum of eight slots.
Player loadouts are fixed at two Plasmid Slots per loadout.