Abstract. Nonnegative bivariate interpolants to scattered data are constructed using some C 1 macro-element spline spaces. The methods are local, and rely on adjusting gradients at the data points to insure nonnegativity of the spline when the original data is nonnegative. More general range-restricted interpolation is also considered.Keywords: spline interpolation, shape preservation, nonnegative surfaces §1. IntroductionInterpolating scattered data is a common problem in a wide range of application areas. It is often required that the interpolant preserves known shape properties inherent to the data. Common shape properties are convexity, monotonicity and nonnegativity. In this paper we consider the nonnegativity-preserving interpolation problem.Problem 1.1. Given a set of scattered data points, find a function s defined on Ω such that s(x i , y i ) = f i for i = 1, . . . , n, and s(x, y) ≥ 0 for all (x, y) ∈ Ω.A standard approach for solving this problem is to work with either polynomial splines [2,5,6,9,16] or rational splines [1,8,11,12,15]. These splines are defined on a triangulation with its vertices at the data points. Problem 1.1 is often solved as an optimization problem in order to find a visually pleasing, nonnegative spline that interpolates the data. Such methods are mostly global in nature, i.e., the spline coefficients globally depend on all of the data. Our aim here is to focus on the construction of local and easy to use methods based on standard C 1 macro-element spline spaces.The paper is organized as follows. In Sects. 2 and 3 we describe nonnegativitypreserving interpolation methods using the C 1 Powell-Sabin and Clough-Tocher macro-elements, respectively. We discuss the approximation order of the methods in Sect. 4, and in the following section we explain how to treat certain rangerestricted interpolation problems. Sect. 6 is devoted to some numerical examples. We conclude with some remarks.