Gelidium latifolium collected monthly at Sinop Peninsula (Black Sea, Turkey) was studied during a 1-year period. Physical and gelling properties of agar extracted from G. latifolium were investigated. Results showed that agar yield was not significantly affected by seasons and ranged from 32.79 +/- 0.78 to 39.26 +/- 0.37%. Quality parameters such as pH, total ash, acid-insoluble ash, and moisture complied with the international standards and acceptance criteria established for agar. High melting temperature (93.86 +/- 0.27 degrees C) and gelling temperature (47.46 +/- 0.20 degrees C) were obtained in autumn. A relatively high viscosity, gel strength was obtained in autumn and during the second half of the year. Lowest acid-insoluble ash (0.012 +/- 0.002%) and moisture (9.276 +/- 0.20%) were obtained in winter, autumn, and spring, respectively. Using G. latifolium from the Sinop Peninsula, good quality of agar with a gel strength ranging from 206.83 +/- 5.36 to 591.85 +/- 2.42 g cm(-2) was obtained, indicating its potential for commercial exploitation. The highest hysteresis temperature was obtained during summer with a maximum in June (48.63 +/- 0.18 degrees C) and a minimum in autumn (46.20 +/- 0.09 degrees C). Results of this study indicate that the best quality agar was obtained during the second period of the year and in autumn. FTIR analysis of agar extracted from G. latifolium showed a fairly constant spectrum that were recorded to contain high gel strengths and low sulfate residues. We conclude that the extracted agar is of good quality agar and may have the potential for commercial agar production.