The effect of guar gum preparation on the glycemic control of 12 pregnant insulin-dependent diabetic patients was investigated. The study was performed on inpatients and lasted 3 wk (from week 32 of pregnancy and onward). Weeks 32 and 34 were control periods during which time the patients had their normal diet only. During week 33, the diet was supplemented with guar. The mean blood glucose level of week 33 was 14% lower than that of week 32 (P less than 0.01) but equal to that of week 34. Mean fluctuations of blood glucose during individual days of the 3 wk were similar. The M-value declined significantly from week 32 to week 33, but the M-value of week 33 was not different from that of week 34. The average 24-h glycosuria declined by 63% from week 32 to week 33 (P less than 0.05), whereas the values of weeks 33 and 34 were not significantly different. The mean daily insulin doses of weeks 32, 33, and 34 were similar. The results show that whereas admission of pregnant insulin-dependent diabetic women to a diabetes ward exerts a favorable influence on diabetes control, no further improvement is obtainable if the diet is supplemented with guar.