The use of angular information in the form of line-of-sight (LOS) measurements from passive sensors for the purposes of target localization and tracking has been extensively studied. Previous work has shown that the formation of fused composite measurements from a minimum number of LOS measurements (two) is statistically efficient, and therefore, the Cramer´-Rao Lower Bound (CRLB) pro-vides a valid measurement noise covariance for the resulting composite measurement. If the LOS measurements are not synchronized, however, the formation of composite measurements is not possible from two LOS observations. In this paper, two methods are presented for forming composite measurements when LOS observations are obtained asynchronously. It is demonstrated that the minimum number of LOS measurements required from two asynchronous sensors is four, and that both methods provide a statistically efficient estimate for track initialization.