Environmental context: Microplastics are a new source of toxic compounds in marine and freshwater environments. This research documents the discovery of microplastic fibres in the seawater column and the chemical analysis of associated toxic chemicals in microplastic marine debris. Microplastic pollution is pervasive and hazardous. Initial studies of floating plastic debris in the oceans dealt with macroscopic particles. This research found microscale plastic present as well. Chemical analysis of sorbed materials revealed toxic materials associated with the microparticles. Seawater and plastic fragment samples were collected in September 2007 in the North Pacific Central Gyre. Polycyclic aromatic hydrocarbons and polychlorinated biphenyls (PCBs) were detected by mass spectrometry in extracts from the plastic fragments. Net concentrations of PCBs ranged from 1 to 223 ng g–1 plastic. The most common synthetic polymers were found to be polypropylene and polyethylene. Microscopic plastic fibres and particles were also discovered in the seawater samples and examined by scanning electron microscopy. Analysis of filtered seawater samples also revealed toxic materials in concentrations lower than found on the plastic particles.