The launch forms part of Procter & Gamble's revamp of the Ariel brand under the new strapline 'Pure Clean' as it seeks to take advantage of falling sales at rival Persil (Marketing 2 November).
Slow sales of the UK's top two laundry brands were attributed to a lack of innovation in Marketing's Biggest Brands survey (Marketing, 24 August).
The launch follows P&G's extension of its Flash brand last year with the introduction of the Flash Mark & Stain Eraser, designed for household surfaces.
Homepride also launched a stain remover last year under the Erase Away brand.
The Stain Pen will be available from later this month, priced £2.99.