Naturally occurring foam constituent and surfactant proteins with intriguing 
structures and functions are now being identified from a variety of biological 
sources. The ranaspumins from tropical frog foam nests comprise a range of 
proteins with a mixture of surfactant, carbohydrate binding and antimicrobial 
activities that together provide a stable, biocompatible, protective foam 
environment for developing eggs and embryos. Ranasmurfin, a blue protein from a 
different species of frog, displays a novel structure with a unique chromophoric 
crosslink. Latherin, primarily from horse sweat, but with similarities to 
salivary, oral and upper respiratory tract proteins, illustrates several 
potential roles for surfactant proteins in mammalian systems. These proteins, 
together with the previously discovered hydrophobins of fungi, throw new light 
on biomolecular processes at air-water and other interfaces. This review 
provides a perspective on these recent findings, focussing on structure and 
biophysical properties.