Sixty patients (mean age 80 years) with cognitive impairment who required parenteral fluids for at least 48 h were randomized to receive either intravenous (i.v.) or subcutaneous (s.c.) fluids. There was no significant difference in the mean volume of fluid prescribed over 48 h in the two groups (s.c. 3.3 litres vs. i.v. 3.6 litres) or in the proportion of prescribed fluids actually administered (s.c. 0.82 vs. i.v. 0.76). After adjusting for baseline differences, there was no difference between serum urea or creatinine levels in the two groups at 48 h. Agitation related to the infusion was reported in 11 (37%) patients receiving s.c. fluids and 24 (80%) patients receiving i.v. fluids (p < 0.005). The cost of the cannulae used during the study was 6.80 pounds for the s.c. group and 28.70 pounds for the i.v. group. Local oedema was noted in 2 patients in the s.c. group and led to re-siting of the infusion in 1 patient. No other complication was noted. These results suggest that s.c. fluid therapy is the treatment of choice in nonurgent situations for confused patients who require parenteral fluids.