The effect of season on yield and physical properties of agars extracted from Gracia gracilis and G. bursa-pastoris were determined. The agar yield from G. gracilis was maximum during spring (30%) and minimum during autumn (19%). In G. bursa-pastoris, the agar yield was greatest in summer (36%) and lowest in winter (23%). Agar yield from G. bursa-pastoris was positively correlated with temperature (r = 0.94; P < 0.01) and salinity (r = 0.97; P < 0.01) and negatively with nitrogen content (r = -0.93; P < 0.01). Agar gel strengths fluctuated from 229 to 828 g cm(-2) and 23 to 168 g cm(-2) for G. gracilis and G. bursa-pastoris, respectively. The gelling temperature showed significant seasonal variation for both species. Chemical analysis of agar from the two seaweeds indicated variation in 3,6-anhydrogalactose and sulfate content (P < 0.01). Furthermore, there was an inverse correlation between the two chemical variables. In general, agar extracted from G. gracilis possessed better qualities than agar extracted from G. bursapastoris and can be considered a candidate for industrial use. (C) 2003 Elsevier Ltd. All rights reserved.