The influence of tomatoes on viscosity of aqueous okra suspensions was investigated.The results indicate that tomatoes reduce okra viscosity by accentuating the acidity of the homogenate and by diluting the medium. Loss of viscosity was enhanced by increases in temperature and ionic strength of the homogenate. To minimise this loss, okra suspensions should be prepared with minimal salting, and tomato should be added in a concentrated form. In the tropics, okra (Abelmoschus esculentus L) and tomato (Lycopersicon esculentum Mill) are foods valued highly by consumers. Okra is liked for its 'okra effect', a smoothness that facilitates swallowing of rough-textured foods, and tomatoes for their flavour and nutritional attributes (Kadans 1973; Janick et a1 1981). Okra suspensions lose much smoothness when mixed with tomatoes. This phenomenon has an important bearing on consumer preference dictated by the intensity of the 'okra effect' but its chemical and physical bases remain poorly understood. In this study, viscosity measurements are used as indices of the 'okra effect' in experiments aimed at improving understanding of okra-tomato interactions.Okra and ripened tomatoes were purchased fresh and stored at -15°C in polythene film bags. For use the fruits were thawed, cut into small bits and homogenised separately in a Waring blender. Filtrates were obtained by subjecting the homogenates to gravity filtration, with Whatman No 1 filter paper in the case of tomatoes and through one layer of muslin cloth for okra. All pH measurements were performed using clear filtrates. Titrateable acidity was measured by titration against 0.1 M NaOH and expressed as g kg-' anhydrous citric acid (Pearson 1973). Dynamic viscosity measurements were performed with an Ostwald-type capillary * To whom correspondence should be addressed. 283 J Sci Food Agric 0022-5142/90/$03.50 0 1990 SCI. Printed in Great Britain