Increased menstrual blood loss (MBL) associated with intrauterine device (IUD) use may precipitate or aggravate iron deficiency anaemia, adversely affecting the health of women particularly those from developing countries. Studies were conducted to define the association of MBL and iron status in South American women; to determine the level of MBL induced by IUD use which would result in iron depletion, the length of time for this depletion to occur and, comparing various IUDS, to determine if any currently tested IUDs are suited to long-term use in South American women. A total of 395 women received one of 5 types of IUDs in Santiago, Chile, and Juiz de Fora, Brazil: Lippes Loop, Multiload-250 and Multiload-375 were used in both centres; in Santiago some subjects received the Copper-7 or ProgestasertR devices and in Juiz de Fora, the TCu 200 and the T-Chloroquin IUDs were also tested. MBL and haemoglobin (HGB) were measured for 3 menstrual cycles before insertion, and following insertion, at one, two, four, six, nine, twelve, eighteen and twenty-four months in the majority of cases. Serum ferritin was measured before insertion and at intervals of six months. Mean values of MBL prior to IUD insertion in both centres varied from 21-30 ml. As with previous publications, the use of the Lippes Loop was associated with the greatest increase in MBL which was sustained throughout the 24 months of observation. Women who had one of the two types of Multiload devices inserted also had increased MBL and reduced ferritin for at least 12 months of use. TCu 200 and Copper-7 IUD users had an initial increase in MBL of 1 to 17 ml in the first six months of observation returning to normal levels beyond six months. Serum ferritin levels were lower for one year and then returned to admission values. ProgestasertR users confirmed previous reports of a reduction of 40-50% in MBL and an increase in serum ferritin. Few significant changes in haemoglobin (HGB) concentrations were found. Serum ferritin levels on admission ranged from 7.1 to 16.4 ng/ml in Santiago and from 15.8 to 23.2 ng/ml in Juiz de Fora. Many women were in a marginal state of iron balance as evidenced by lower serum ferritin values. Changes in serum ferritin were very closely related to those in MBL.(ABSTRACT TRUNCATED AT 400 WORDS)