public function getFriendshipsLookup($screen_name = null, $id = null)
	{
		// Check the rate limit for remaining hits
		$this->checkRateLimit('friendships', 'lookup');

		$data = array();

		// Set user IDs and screen names.
		if ($id)
		{
			$data['user_id'] = $id;
		}

		if ($screen_name)
		{
			$data['screen_name'] = $screen_name;
		}

		if ($id == null && $screen_name == null)
		{
			// We don't have a valid entry
			throw new \RuntimeException('You must specify either a comma separated list of screen names, user IDs, or a combination of the two');
		}

		// Set the API path
		$path = '/friendships/lookup.json';

		// Send the request.
		return $this->sendRequest($path, 'GET', $data);
	}