The presence of ESBL/AmpC-producing Enterobacteriaceae in healthy. livestock, such as pigs, was frequently reported worldwide in the last years. The development and potential spread of these resistant microorganisms in farm animals is discussed critically.Therefore, the main objectives of this longitudinal study were to determine potential sources and prevalence dynamics of ESBL/Amp-Cproducing Escherichia coli in seven German ESBL/AmpC-positive conventional fattening pig farms in the course of the fattening period. Samples tested were taken at three different times within one finishing fattening period and included 20 individual faeces samples as well as various samples of the animals' housing environment such as pooled faeces, boot swabs, dust and environmental swabs. In individual faeces average carriage levels of 45%, 29% and 36% at the three sampling times were accompanied by decreasing faecal counts from 2.97 x 10(4) cfu/g at the first to 2.17 x 10(3) cfu/g at the third visit. In the animals' housing environment 47.6% of pooled faeces and boot swab samples respectively and 5.9% of environmental swabs but none of the dust samples were tested positive. Altogether 228 E. coli isolates were analysed by combination disc tests, PCR and partly via sequencing. Thereby, a novel gene bla(TEM-206) was detected. This study shows different detection levels of ESBL/AmpC-producing E coli amongst the different farms and in the course of the fattening period. Pooled faeces and boot swab samples but not dust samples seem to be appropriate to assess the herd status of pigs with respect to ESBL/AmpC-producing Escherichia coli.