The divestiture, which is being managed by the Credit Suisse Group, will see the sale of around 7.8 million shares held by Blackstone's BCP Murano II Sarl holding company to a variety of institutional investors.
The move is expected to generate $386m for Blackstone based on Gerresheimer's most recent valuation.
Axel Harberg, CEO of the Dusseldorf-headquartered packaging firm, said that: " Blackstone made a successful IPO possible and afforded us enormous growth opportunities.
With this exit, our free float rises substantially, making our shares even more attractive to the investment community ."
Initially, news of the decision saw Gerresheimer's share price fall 1.4 per cent to €33.26, giving the company a market value of €1.04bn.
Subsequently, however, the reaction has been more positive.
Commerzbank AG analyst Daniel Wenderoff, for example, told Bloomberg that " the market has expected [that] the 25 per cent Blackstone stake would be sold ," and speculated that this had caused potential investors to hold back.
He issued a "buy" rating for the German firm.
Gerresheimer's positive first quarter Blackstone purchased Gerresheimer from Investcorp and JP Morgan in 2004 for a reported $700m, subsequently taking it public in an IPO on the Frankfurt stock exchange in 2007.
Earlier this month Gerresheimer reported a first quarter profit of €2.5m, up from the €4m loss is saw in the comparable quarter last year.
The firm explained that higher sales by its life science and pharmaceuticals divisions, particularly of plastic products, had been a key growth driver.
In contrast Blackstone, which invests in firms operating in a wide range of sectors from pharmaceuticals to financial services, revealed that its fourth quarter earnings for 2007 were down 89 per cent to $88m. The group is yet to report its financials for the first quarter of the current year.
Gerresheimer plans to expand Pfreimd site Shortly after the Blackstone decision, Gerresheimer announced plans to expand its medical technology site at Pfreimd in southwest Germany.
The facility, which is run by the group's Gerresheimer Wilden division, manufactures a variety of medicinal products, including dry-powder inhalers, components for syringe systems and devices for the diabetes market.
Gerresheimer said that the expansion project, which will created around 100 new jobs, will equip the site with an 8,700 square meter ISO class 8 accredited clean room and a 5,400 square meter controlled area.
In a joint statement, Klaus Walber and Manfred Baumann managing directors of Gerresheimer Wilden said that: " the Pfreimd location is of existential importance to us ," and added that the step by step expansion of the site will continue through to 2010.
The firm also announced that the plant has received accreditation to manufacture medicinal products for the Japanese market in collaboration with the Roche's diagnostics division.