A prototype lying mat as an alternative to straw bedding for improving sow lying comfort was evaluated using a dynamic group of 47 gestating sows housed in a pen with 5 communal lying areas. Mats were installed in 3 lying areas while the concrete floors of the remaining lying areas remained uncovered (period 1). After 5 weeks the position of the lying mats was rotated (period 2). 24 h image-recordings were made from 5 weeks prior to the installation of the mats (period 0) until 5 weeks after rotation of the mats. The effect of the mats on lying area occupancy and behaviour was analysed. The occupancy of lying areas with a mat increased as compared to both the same lying areas before the installation of the mats (period 0), and to the other lying areas without a mat during the same observation period (periods 1 and 2, P = 0.011). This preference was more pronounced amongst sows that had been habituated to the experimental set-up for more than 7 days (P <0.001) and in period 2 than period 1 (P = 0.004). However, the effects of period, stocking density and ambient temperature were confounded and could not be determined unambiguously. Mats did not significantly affect activity (proportion of time standing, sitting, and lying), lying bout duration, duration of lying per lying posture (sternal, half recumbent, recumbent) or getting-up duration. Sows lying on mats as compared to concrete, however, changed lying posture more often (P = 0.002) and were more likely to adopt a recumbent instead of sternal lying posture (P = 0.003). Under conditions of this experiment covering concrete floors with synthetic mats appeared to improve sow lying comfort. It is questionable whether this finding can be generalised to other (climatic) conditions. Furthermore, before such mats should be considered as an alternative to straw bedding for improving lying comfort further research is warranted to improve the durability of the mats and to investigate the long-term health consequences. (C) 2008 Elsevier B.V. All rights reserved.