On the basis of a retrospective study of 71 children followed for 24 months after diagnosis of type I insulin dependent diabetes a fitted mathematical model was constructed for the prediction of the course of beta cell function from the time of diagnosis. Two equations were derived, one for the maximal basal (B-max) and the other for the maximal i.v. glucagon stimulated peak C-peptide (P-max) levels reached during the remission period. The prognostic variables selected for analysis were: peak C-peptide levels at diagnosis (Po), age sex, degree of obesity, pubertal rating, the presence of islet cell antibodies (ICA) and levels of GHb. Multivariate analysis of the data showed that Po (p = 0.0006), puberty (p = 0.041). obesity (p = 0.0021), sex (p = 0.031), ICA (p = 0.0045) and GHb(p = 0.0066) significantly contributed to the prediction formula obtained for B-max whereas the contribution of the above variables for P-max were: Po (p = 0.0019), puberty (p = 0.0187), obesity (p = 0.0058), sex (p = 0.0598), ICA (p = 0.0187) and GHb (p = 0.0027). The residuals of the observed values from the values fitted by the predicted equations served to define two separate groups demonstrating distinct differences in the natural course of beta cell function in type I diabetes. This fitted model may thus be useful in distinguishing between newly diagnosed young patients who will undergo remission, requiring lower insulin doses, and those who have little chance for remission. It might also be helpful in the selection of patients most likely to benefit from immunosuppression or modulation, to maximize the benefit to risk ratio for such patients.