We have previously shown that olfactory bulbectomy causes a decrease in some metabolic parameters of chelonians. In the present study we evaluate the capacity for water retention of normal land tortoises and of tortoises with long-standing olfactory bulbectomy. Adult male Geochelone carbonaria tortoises were divided into three groups: group B, 11 tortoises submitted to olfactory bulbectomy two years prior to the study; group PB, 7 tortoises submitted to pseudobulbectomy two years before the study; group N, 9 intact animals. The animals were maintained in captivity in an outdoor area and submitted to the present study under semi-laboratory conditions involving an 18-day period with no solid or liquid food followed by 4 days of free water ingestion and a subsequent 17-day period of no solid or liquid food ingestion. Before water was offered, mean body weight (+/- SEM) was 1764 +/- 93.5 g for group B, 1801.4 +/- 137.4 g for group PB, and 2077.8 +/- 288.8 g for group N. Animal weight was recorded again on the 2nd and 4th days of water ingestion and on the 3rd, 5th, 7th, 10th, 12th, 14th and 17th days of fasting. Since no differences were detected between PB and N animals at any time, the data for the two groups were pooled. Thus a control group (C) of 16 animals was used for statistical comparison. The data reflect three behavioral situations: 1) water ingestion and urine excretion, 2) no water ingestion and urine excretion, and 3) neither water ingestion nor urine excretion.(ABSTRACT TRUNCATED AT 250 WORDS)