Campaigners against genetically modified crops blocked the main entrance of a multi-national company's Cambridgeshire base on Friday.
Bayer produces seeds and crops
About 15 protesters gathered outside Bayer CropScience in Hauxton,
near Cambridge, where genetically modified plants are developed and tested.
A Cambridgeshire Police spokeswoman said officers were at the scene, where the protest started at about 0800 BST. No-one was arrested.
The protesters were preventing gates from being opened, and lorries and people from getting in and out of the site, she said.
Anti-GM campaigner John Green said five of them were locked together with handcuffs inside steel tubes.
Another was chained to the underside of a lorry which was blocking the entrance, he said.
Mr Green, 28, from Sheffield, South Yorkshire, said that 85% of GM crop trials in the UK in 2002 involved seed owned by Bayer.
"We are here because its parent company Bayer AG based in Germany is this morning holding its annual general meeting for shareholders and other GM activists have gone to Cologne to to show that GM crops are not welcome here,"
Protesters were also waving banners and handing out leaflets.
The German drug and chemical giant Bayer produces pesticides, insecticides and herbicides and develops seeds and crops.
Non-one from Bayer was available for comment.