Forty-four (32.8 per cent) of 134 patients[see figure in the PDF file]treated continuously with guanethidine for a period of at least 12 months developed recognizable fluid retention.Previous edema may be a predisposing factor and fluid retention occurred more commonly in women. Neither of these factors offers a complete explanation of this side effect.No evidence has been found to suggest that fluid retention occurs preferentially in patients with renal or cardiac insufficiency. The findings are compatible with a universal fluidretaining influence of guanethidine presenting as a graded phenomenon.